Decrease In Sedimentation Rate Research Articles

Ribonucleic acid is a component of the oligomeric, transformed mouse AtT-20 cell glucocorticoid receptor.

The glucocorticoid receptor from mouse AtT-20 pituitary tumor cells exists in three forms. The largest form is an untransformed (non-DNA-binding), oligomeric species (9.1 S, 8.3 nm, Mr 319 000). Two transformed (DNA-binding) forms can be generated. One is an oligomeric protein (5.2 S, 6-8.3 nm, Mr 132 000-182 000), while the other is the monomeric, hormone-binding subunit (3.8 S, 6 nm, Mr 96 000). The composition of the oligomeric, transformed receptor and its relationship to the monomeric protein were examined. The 3.8S monomer can be isolated from DEAE-cellulose (0.12 M step elution) in a form that continues to sediment at about 3.8 S on molybdate-containing sucrose gradients and at about 4.2 S on molybdate-free gradients. Addition of a non-hormone-binding component isolated from the same DEAE-cellulose column (0.5 M KCl step) can apparently interact with the 3.8-4.2 S monomer, increasing its sedimentation coefficient to 5.2 S (on molybdate-containing gradients) or 6.6 S (on low-salt, molybdate-free gradients). This factor is a macromolecule (nondialyzable) and is heat-stable (100 degrees C, 20 min). A dose-dependent shift to the higher sedimentation coefficient is observed when increasing quantities of the 0.5 M step material are added to the receptor monomer. This activity is abolished when the 0.5 M step material is treated with ribonuclease A. Further, when RNA is purified from the 0.5 M step by phenol/chloroform extraction, its ability to increase the S value of the monomer is retained. Ribonuclease treatment of the untransformed, 9.1S, oligomeric complex does not cause a significant decrease in sedimentation rate, while the same treatment of the 5.2S, oligomeric, transformed receptor (obtained after Sephadex G-25 transformation) causes a decrease in sedimentation rate to about 3.8 S. The addition of bovine liver mRNA and rRNA does not cause a shift in sedimentation rate of the receptor monomer to a discrete, higher sedimenting receptor form. However, the addition of total rabbit liver tRNA or three distinct tRNA species causes a shift in sedimentation to a similar, but not identical, form as that with the 0.5 M step material. We propose that the 5.2S, oligomeric transformed glucocorticoid receptor is composed of one monomeric hormone-binding, protein subunit (Mr 96 000) and a low molecular weight RNA (Mr 36 000). This interaction may be important for the role of the receptor in regulating gene expression.

Changes of laboratory variables with time in cirrhosis: Prognostic and therapeutic significance

The time change of laboratory variables in cirrhosis was studied by analysis of data from 488 patients with cirrhosis included in a controlled clinical trial of long-term prednisone vs. placebo. In the placebo group, a marked regression towards normal was seen within 3 months of entry into the trial (increase in serum albumin, acetylcholinesterase, cholesterol, hemoglobin and decrease in erythrocyte sedimentation rate). The subsequent course did not show a clear pattern, except for a slight increase in serum bilirubin and decrease in albumin. When studied in relation to the time of death in patients dying from a "hepatic" cause, marked increase in bilirubin and decrease in prothrombin index, albumin and cholesterol were seen in the year prior to death with little change before that time. In the prednisone group, a more marked decrease in bilirubin, SGOT, alkaline phosphatase, gamma-globulin, sulfobromophthalein retention, erythrocyte sedimentation rate and increase in leukocytes, prothrombin index and cholesterol were seen during the first 3 months. In relation to time of death from a "hepatic" cause, similar changes were seen as in the placebo group except that alkaline phosphatase increased and cholesterol did not decrease. A beneficial effect of prednisone on survival, as expressed by a previously developed therapeutic index, was associated with decrease in SGOT, alkaline phosphatase and gamma-globulin within the first 3 months. An increase in SGOT during prednisone seemed to be associated with harmful effects of therapy.

Suspended Particulate Loading on the Macrobenthos in a Highly Turbid Fjord: Knight Inlet, British Columbia

Knight Inlet is a deep, low-energy but well-oxygenated fjord. The effects of turbidity are principally those of seasonally very high vertical flux from the sediment-laden surface layer. Submersible observations of the benthos are related to suspended load and sedimentation rate data. The bayhead delta slope receives a continual rain of glacial silt (30 cm/yr) and has summer sedimentation rates of 4 kg∙m−2∙d−1.The epifauna of the steep fjord walls shows a marked down-inlet increase in abundance, and the number of species increases from 9 to 45. Brachiopods (Laqueus californianus), solitary corals (Caryophyllia/Cyathoceros), and encrusting sponges are remarkably tolerant of high turbidity. The high sedimentation rates affect the epifauna in three ways: (1) subjection to the ubiquitous "gentle rain" of floes and agglomerates; (2) more locally, microturbidity flows set off by biological resuspension of unstable slope sediment; and (3) major slides of rock and/or sediment. Submarine soil-creep limits the slope infauna, by burrows requiring repeated reexcavation.Down-inlet decrease in sedimentation rate is accompanied by a change in feeding type. In the upper inlet, suspension feeders taking particles < 8 μm (e.g. sabellids, brachiopods) probably utilize bacteria associated with the high vertical flux of SPM. In the middle inlet, selective suspension feeders (e.g. crinoids, gorgonians) sort the SPM for larger particles. In the lower inlet, filter feeders (e.g. barnacles, glass sponges) increase, especially where currents are stronger. The soft-bottom detritus feeders also show a change: from epibenthic forms (e.g. pandalid shrimp, spider crabs) in the upper inlet, through burrowing shrimp in the middle inlet, to ophiuroids in the lower inlet. These changes are correlated with the greater amounts of organic carbon preserved in bottom sediments as they are less diluted by glacially derived inorganic material.The modern-day "turbid association" of brachiopods, solitary corals, and sponges recalls typical outer shelf-basinal shale facies of the Palaeozoic. Turbid, low-energy environments were thus colonized early but faunas have since become less diverse.Key words: fjord, benthos, sedimentation, submersible

Early experiences with auranofin in juvenile rheumatoid arthritis

Pharmacologic management of juvenile rheumatoid arthritis is only one of several modalities necessary for effective control. The stepping stones to proper management Include a planned long-range program, physical therapy with swimming, good health habits, and consultation with other health professionals who are part of the management team. Pharmacologic therapy includes nonsteroidal anti-inflammatory drugs initially, occasionally corticosteroids, and slow-acting antirheumatic drugs, including injectable gold when therapeutic response is inadequate. Early experiences with oral gold are reported here. Auranofin (triethylphosphine gold) was administered to 21 patients with juvenile rheumatoid arthritis during a segment I, open ended, open-label, noncontrolled trial designed to establish safety and preliminary efficacy. Initial dosage was 0.1 mg/kg per day; incremental increases to 0.2 mg/kg per day were allowed (with usual increase to 0.15 mg/kg per day). Aspirin (80 mg/kg per day) or tolmetin (20 to 40 mg/kg per day), or naproxen (400 to 600 mg/m 2 per day) were allowed as rapidly acting anti-inflammatory agents. Stable measurable plasma concentrations of gold were attained in all patients during the study. More than half the patients sustained clinically significant improvement (greater than 25 percent) with regard to the number and severity of joints with swelling, pain on motion, and tenderness. In nine of the 19 patients, the total number of joints with active arthritis decreased by at least 25 percent. All articular disease indices measured indicated improvement of group mean changes between the initial and final visit. Eleven of 16 patients with an elevated erythrocyte sedimentation rate showed decreases of at least 25 percent. The group given higher dosages had a greater proportion of responders in regard to decreases in erythrocyte sedimentation rate (nine of 11 patients). Four of six patients whose serums contained rheumatoid factor showed decreases in the titers. Discontinuation of auranofin was necessary in two patients: one because of headache and one because of hematuria and anemia associated with a severe flare-up of polyarticular disease. The results from this trial reveal sufficient patient improvement to plan a double-blind trial of auranofin in children with juvenile rheumatoid arthritis.

Auranofin in the treatment of juvenile rheumatoid arthritis

Auranofin (triethylphosphine gold) was administered to 21 patients with juvenile rheumatoid arthritis during an open-ended, open-label, noncontrolled trial designed to establish safety and preliminary efficacy. Initial dosage was 0.1 mg/kg/day; incremental increases to 0.2 mg/kg/day were allowed. Aspirin (80 mg/kg/day), tolmetin (20 to 40 mg/kg/day), and naproxen (400 to 600 mg/m2/day) were allowed as rapidly acting anti-inflammatory agents. All patients attained measurable plasma concentrations of gold during the study. Clinically significant improvement (greater than 25%) occurred in more than half the patients with regard to the number and severity of joints with swelling, pain on motion, and tenderness. The number of joints with active arthritis decreased by at least 25% in nine of the 19 patients. Group mean changes between the initial and final visit indicated improvement in all articular disease indices measured. Eleven of 16 patients with an elevated erythrocyte sedimentation rate showed decreases of at least 25%. The group given the higher dosage had a greater proportion of responders with decreases in erythrocyte sedimentation rate. Four of six patients whose sera contained rheumatoid factor showed decreases in its titer. Discontinuation of auranofin was necessary in two patients because of headaches and because of hematuria and anemia associated with a severe flare of polyarticular disease, respectively. The results from this trial are sufficiently encouraging to merit a double-blind trial of auranofin in children with juvenile rheumatoid arthritis.

Eocene-Oligocene Sea Level Changes as Reflected in Alabama Outcrop Sections: ABSTRACT

Outcrops at Little Stave Creek and St. Stephens Quarry in southwestern Alabama contain continuous sections across the Eocene-Oligocene boundary. The sequence of lithologic and biologic changes recorded across the boundary in Alabama can be best explained by a rising sea level. From the base to top, the sequence consists of: silty glauconitic marl (Pachuta); glauconite marl (Shubuta); thin glauconitic clay (unnamed); glauconitic clay and marl (Red Bluff) interbedded with silty limestone (Bumpnose); and grading upward into a carbonaceous clay (Forest Hill). The last occurrence of the planktonic foraminifera Globorotalia cerroazuleisis cocoaensis occurs just below the top of the Shubuta marl. The last occurrence of the calcareous nannofossil Discoaster saipanensis is within he Pachuta. Lithologic and paleontologic studies indicate that the Pachuta-Shubuta units represent a deepening-upward sequence. As water depths increased, the locus of terrigenous deposition moved updip or shoreward of the sections at Little Stave Creek and St. Stephens Quarry, resulting in the production of a compressed marine sequence capped by a nondepositional marine hiatus. During and after the period of deepest water, renewed terrigenous deposition resulted in a shallowing upward sequence (Red Bluff, Bumpnose, and Forest Hill). We suggest that: (1) the changes in water depth and sedimentation in the Alabama sections occurred as a result of a rapid rise in relative and eustatic sea level (Pachuta, Shubuta), reaching a maximum during the time of deposition of the unnamed blue clay, followed by a period of less rapid relative rise and slow eustatic fall (Red Bluff, Bumpnose, Forest Hill); and (2) the decrease in sedimentation rates (and hence a decrease in stratigraphic resolution) caused by a rapid rise of eustatic sea level may also account for the apparently synchronous first and last appearances of a number of microfossil lineages at the Eocene-Oligocene boundary in Alabama and elsewhere. End_of_Article - Last_Page 506------------

Environments and Dynamics of Clastic Sediment Dispersal Across Cambrian of Grand Canyon: ABSTRACT

End_Page 1004------------------------------The transgressive Grand Canyon Cambrian contains basal fluvial sands (Tapeats Sandstone) and overlying shallow marine sands and shales (Bright Angel Shale) in which textures and structures permit a detailed reconstruction of clastic sediment dispersal across a broad cratonic margin. Dominantly trough cross-bedded basal Tapeats Sandstone, containing buried regolith in bed-rock depressions, a low-variance, unimodal paleocurrent trend down the regional paleoslope, and well to moderately sorted medium to coarse-grained sands, records pre-vegetation bed-load fluvial sedimentation. Bed-load sands (> 200 mµ) mature from arkosic to orthoquartzitic within 5 to 10 m of the base. Finer, suspension-transported sands remain subarkosic through the entire 250 to 500 m of Cambrian section implying rapid dispersal. The Bright Angel Shale is composed of shallowing upward sedimentary cycles 1 to 6 m thick. Lower parts of the cycles are thinly interbedded fine sand and shale layers whose sedimentary structures and textures record level-bottom storm resuspension, dispersal, and deposition (sand layers) alternating with quiescent periods of finer silt and clay dispersal and accumulation. Bed-load transported sands are absent. Sand bed thickness up to a maximum (5 to 20 cm) represents variation in storm intensities with maximum thicknesses controlled by water depth, which limits volume in suspension. Upper parts of cycles are cross-laminated fine sands with glauconite and U-shaped or vertical burrows. These represent shoaling phases with increased bottom agitation, decreased sedimentation rate, and winnowing bypass of silts and clays. Organism structures, tadpole ripples, and rare mud cracks record shallowing. Cycle caps are 1 to 20-cm thick layers of medium to very coarse quartz sand, hematitic ooids, phosphatic, and dolomite cemented clasts that record phases of emergence and complete bypass of all suspension load. Recently recognized dunes 3 to 5 m in height provided bed load dispersal at the close of sedimentation cycles. Structures and textures suggest dunes are eolian. End_of_Article - Last_Page 1005------------

Geochemical Evidence for Modern Sediment Accumulation on the Continental Shelf off Southern New England

ABSTRACT An area of fine-grained sediment approximately 170 km 74 km in size, located in water depths between 60 m and 150 m, south of Martha's Vineyard, Mass., is a site of modern sediment deposition. The 14C ages systematically increase with sediment depth from about 1,300 years B.P. at the surface to 8,000-10,000 years B.P. at the depth of maximum core penetration. The old age for the surface sediments probably results from a combination of deposition of old carbon and faunal mixing. In the finest sediments, the sedimentation rates were approximately 130 cm/1,000 yrs when deposition began and have decreased to about 25 cm/1,000 yrs. The decreasing sedimentation rate reflects a diminishing source of fine sediments, which presuma ly came from the Georges Bank and Nantucket Shoals area. Inventories of excess 210Pb in undisturbed cores average 70 dpm/cm2 (disintegrations per minute per square centimeter), more than two times higher than the flux of 210Pb from the atmosphere and from 226Ra decay in the overlying water. This additional influx of 210Pb either must be with new fine-grained sediment material or from solutions that are stripped of their 210Pb by particulates in the bottom nepheloid layer. Stable Pb concentrations in surface sediments are about 28 ppm, as much as two times higher than concentrations at depth. The high accumulation rates, 210Pb inventories, and trace-metal profiles imply that this area is a modern sink for fine-grained sediments and for pollutants associated with particulate matter in the water column. To our knowledge, this is the only site of present-day natural deposition on the Continental Shelf off the eastern United States, exclusive of the Gulf of Maine. Because the net currents on the outer half of this Continental Shelf flow from northeast to southwest, this fine-grained deposit may receive its sediments and possible contaminants from the Nantucket Shoals and Georges Bank regions.

Geologic and Geophysical Investigation of Part of Outer Continental Shelf and Upper Continental Slope, Northwest Gulf of Mexico: ABSTRACT

The continental slope in the northwest Gulf of Mexico ranges in width from 110 km (59 nmi) off the Rio Grande to 240 km (130 nmi) off Louisiana. Throughout its Cenozoic history, this continental margin has increased its limits through the progradation and aggradation of clastic sediments on a broadly downwarped and subsiding basement. Eustatic changes in sea level in response to Pleistocene climatic fluctuations have provided for the deposition of these transgressive and regressive deposits. Rapid Pleistocene sea-level changes are responsible for accelerated deposition and extension of the continental margin. Lowering of sea level moved nearshore sedimentation to the outer edge of the continental shelf. Shelf outbuilding occurred as deltas prograded over the shelf-slope break. Growth faults cut the sediment column in response to this rapid sedimentation. Marine transgression resulted in a decreased sedimentation rate, depositing a transgressive sequence which capped the regressive clastics. The continental slope in the northwest gulf is further marked by diapiric salt uplifts of variable size. Correlation of recent high-resolution seismic profiles with drill-core data in a selected location on the outer continental shelf and upper continental slope off the Texas Gulf coast, together with textural, micropaleontologic, and paleomagnetic information and sparker data, yield a history of the late Pleistocene to recent. Analysis of shelf-edge progradation and its relation to sedimentation and structural activity on the continental slope yield additional information with respect to the Pleistocene to recent depositional history. End_of_Article - Last_Page 687------------

Use of ethidium bromide fluorescence enhancement to detect duplex DNA and DNA bacteriophages during zone sedimentation in sucrose gradients: molecular weight of DNA as a function of sedimentation rate

Duplex DNA molecules and DNA bacteriophages have been sedimented through 5--25% sucrose gradients containing ethidium bromide. The location of DNA within the gradients has been determined by illuminating gradients with ultraviolet light and observing the ethidium bromide fluorescence enhancement induced by the DNA. The relative sedimentation rates of linear, duplex DNAs from bacteriophages T4, T5, T7 and an 8.3% T7 deletion mutant have been determined. The distances sedimented by DNA have been corrected, when necessary, for a progressive decrease in sedimentation rate that occurs after the DNA has traversed 40% of the sucrose gradient. The corrected distances sedimented by two DNA molecules, r1' and r2', are related to the DNA molecular weights, m1 and m2, by the equation: r1'/r2' = (m1/m2)0.38 when 0.025--0.70 microgram of each type of DNA is sedimented. Intact bacteriophages were also sedimented in ethidium bromide--sucrose gradients and detected by fluorescence enhancement.

On the structure of the folded chromosome of Escherichia coli

After careful lysis of exponentially growing Escherichia coli cells, the DNA is released in a highly-folded conformation (Stonington & Pettijohn, 1971), sedimenting as an heterogeneous population of structures with sedimentation coefficients ranging from 1300 s to 2200 s. Chromosomes arrested at initiation by amino-acid starvation sediment as an homogeneous 1300 s species. The gradual bimodal decrease in sedimentation rate seen after amino-acid starvation suggests that the faster sedimenting structures in exponentially growing cells represent the folded chromosomes at more advanced stages in their replication cycle. The folded chromosomes are supercoiled, as evidenced by the biphasic response of their sedimentation rates to increasing concentrations of ethidium bromide. The 1300 s folded chromosome lined up at initiation, as well as the 1300 s to 2200 s replicating chromosomes, have about the same concentration of superhelices as previously observed for intracellular λ and SV40 DNA's, namely, about one negative superhelical turn per 400 base pairs. Kicking with DNase releases these superhelical twists and relaxes the folded chromosome to slower sedimenting forms. However, somewhere between 6 and 40 nicks per DNA strand are required before a fully “relaxed complex” is obtained; this complex sediments 40% slower than the original non-DNase-treated chromosome, but still five times faster than the corresponding unfolded DNA. It appears to have lost all of its superhelical character, since it behaves exactly like linear DNA upon ethidium bromide intercalation. A preliminary model for the folded bacterial chromosome has the DNA looped around a core, probably an RNA species. The RNA-DNA interactions stabilize the folded structure and topologically divide the chromosome into a limited number of loops. There are somewhere between 12 and 80 loops per chromosome, each with the same superhelical concentration. A single-strand nick with DNase allows free rotation of the DNA chains within a loop, eliminating the superhelices of that particular loop without affecting the superhelical content of the rest of the chromosome. The bacterial chromosome can then be seen in three distinct, well-defined conformations, (a) Compact, folded and supercoiled. (b) Relaxed and folded, with no superhelices but retaining its RNA core and DNA loops. This relaxed complex is observed after extensive nicking with DNase, or after eliminating the super-helices by ethidium bromide intercalation, (c) Unfolded chromosome à la Cairns, observed after breaking the UNA core or otherwise disrupting the stabilizing interactions.

Repair of radiation-induced DNA strand scissions in Chlorella during the cell cycle.

In the first part of our studies DNA sedimentation behaviour during a mitotic cycle of the unicellular green algaChlorella pyrenoidosa was investigated. In the S-phase a decrease in sedimentation rate of akaline-denatured DNA could be observed. Alkaline sucrose density gradient analysis was used to examine the repair of radiation-induced single strand breaks in DNA in various stages of the cell cycle. Three characteristic phases of the growth period were chosen: autospore phase, early beginning of DNA replication and maximum DNA synthesis. Our results indicate that DNA damage is different within the cell cycle, but the repair of radiation-induced DNA strand scissions is only to a small degree dependent on the cell stage.

The dissociation of Yoshida hepatoma ribosomes into active particles.

1. The sedimentation pattern of Yoshida hepatoma ribosomes shows mainly a high dimer peak and an intermediate peak between those of monomer and dimer. 2. The treatment of the postmitochondrial supernatant with EDTA or potassium chloride leads to the dissociation of ribosomes into subunits, through a decrease ofthe ribosomal Mg(2+)/phosphorus ratio. Provided that the deprivation of endogenous Mg(2+) is not complete, the subunits reassociate into active polyribosomes after addition of magnesium chloride to the medium. If the Mg(2+)/phosphorus ratio is lowered below 0.01 (mumol/mumol), structural changes occur, that become evident by a loss of protein and by a decreased sedimentation rate, which render the subribosomal particles unable to reassociate. 3. In the re-formation of polyribosomes from subunits, during the progressive increase of the concentration of magnesium chloride in the medium, the formation of monomeric ribosomes seems to be intermediate. 4. A dimerization of monomers and subunits occurs at concentrations of magnesium chloride greater than those required for the re-formation of polyribosomes and a preincubation for 1h at 0 degrees C is necessary for the maximum dimerization, whereas the complete reconstitution of polyribosomes is immediate.

On the mechnaism of radiosensitization by 5-bromouracil. The occurrence of DNA strand breaks in U.V.-irradiated phage T4 as influenced by cysteamine.

Abstract— U.V.‐irradiation of phage T4Bor results in a decrease in sedimentation rate of BU‐DNA which is attributed to single‐ and double‐strand breaks. No breaks could be observed in unsubstituted DNA. Cysteamine present during u.v.‐irradiation is able to prevent double‐strand breaks but does not influence the production of single‐strand breaks measured by alkaline sucrose gradient centrifugation. The biological importance and nature of DNA strand breaks due to BU‐incorporation as well as the action of the protective agent on these breaks and on the biological activity are discussed.

THE DEVELOPMENT OF THE CUTANEOUS MICROVASCULAR SYSTEM IN THE NEWBORN

SUMMARY.– The development of the cutaneous capillaries has been studied in 40 infants aged 1 day to 17 weeks. At birth there is a disorderly capillary network. There is a gradual development to an orderly subpapilliary plexus and papillary loops by 14th–17th week of life. In areas of creases this development is delayed, while in the palms, soles and nail folds there is an early development of capillary loops. An attempt has been made to correlate this development with certain dynamic physiological processes during the neonatal period as well as with exposure to the cold environment. These physiological processes are: (a) increase in skin surface area (b) increased blood viscosity related to (i) increased haematocrit (ii) decreased oxygen tension (iii) low blood pressure (iv) increased transudation of fluid from blood vessels (v) decreased sedimentation rate (vi) decreased red cell flexibility.

The Modification of Yeast Hexokinases by Proteases and Its Relationship to the Dissociation of Hexokinase into Subunits

Abstract Crystalline hexokinase prepared by the method of Darrow and Colowick consists largely of enzyme which has been modified in its chromatographic and electrophoretic behavior by yeast protease which is present during the isolation procedure. This proteolytic modification can be prevented by removal of the protease by chromatography on diethylaminoethyl cellulose; it can also be largely inhibited by phenylmethanesulfonyl fluoride. Preparations made by the diethylaminoethyl cellulose method contain two forms of the enzyme (P-I and P-II), both of which are more basic by chromatography and electrophoresis than is protease-modified enzyme (S forms). Form P-II shows the same catalytic activity as the Darrow-Colowick preparation, but Form P-I is less active. The two forms are equally susceptible to modification by trypsin. Forms P-I and P-II exist mainly as tetramers of molecular weight about 100,000 at low ionic strength in the neutral pH region, as measured by ultracentrifuge, light scattering, or gel filtration. They tend to dissociate, without loss of catalytic activity, to dimers as the ionic strength, temperature, or pH is raised or when glucose is added in the presence of phosphate. They can be converted to S forms by trypsin or yeast protease only when glucose or salts are present, suggesting that the enzyme must be in the dimer state in order for modification to occur. The protease-modified enzyme tends to exist mainly as a dimer of molecular weight around 50,000 at neutral pH. Thus, modification by trypsin seems to remove some groups which normally play a role in the association of dimer molecules to form the tetramer structure. Mercaptoethanol causes a striking decrease in sedimentation rate when added to the enzyme at pH 9.0. This may be correlated with the recent finding that mercaptoethanol can cause inactivation of the enzyme at this pH.

Supercoiled circular DNA-protein complex in Escherichia coli: purification and induced conversion to an opern circular DNA form.

The 23S twisted circular form of ColE(1) DNA has been isolated from Escherichia coli as a tightly associated DNA-protein complex with a sedimentation coefficient of approximately 24S. Treatment of this complex with pronase, trypsin, sodium dodecyl sulfate, Sarkosyl, or heat results in a conversion to a slower sedimenting form of 17S or 18S, as determined by centrifugation in neutral sucrose gradients. These treatments do not alter the sedimentation properties of noncomplexes supercoiled ColE(1) DNA even in the presence of the ColE(1)-protein complex. Electron microscopic analyses indicate that the decrease in sedimentation rate of the ColE(1)-protein complex after treatment with these various agents is largely owing to an induced transition of ColE(1) DNA from the supercoiled to the open circular state.

The soluble hemagglutinins of adenoviruses belonging to Rosen's subgroup 3. II. The slowly sedimenting hemagglutinin.

Zonal centrifugation of soluble components of adenovirus types 1, 2, 5 and 6 revealed five different components that represented, listed in sequence of decreasing sedimentation rate, penton aggregates (rapidly sedimenting complete HA; RHA), hexons, isolated pentons, slowly sedimenting complete HA (SHA) and fibers.

Size and shape of isolated rat liver mitochondria.

The dimensions of unfixed rat liver mitochondria, isolated in 0.44 M sucrose, were measured on photomicrographs taken by phase-contrast microscopy. The lengths ranged from the limit of resolution of the microscope (ca. 0.2 μ) to ca. 5 μ. The smallest measured particle had a calculated volume of 0.008 μ3 and the largest 3.85 μ3. Separate fractions of mitochondria, in order of decreasing sedimentation rate and fragility (Can. J. Biochem. 44, 497), were found to range in mean size from 0.92 μ long × 0.59 μ in diameter (fraction I), through 0.84 μ × 0.59 μ (fraction III) to 0.60 μ × 0.48 μ (fraction V). The limitations and errors in the measurements have been discussed. While these measurements cannot be considered "correct" in an absolute sense, they more closely represent the actual size of unfixed isolated mitochondria than do previously reported measurements, and reliably allow size characterization of different fractions.

Accretion rate of cosmic matter from iridium and osmium contents of deep-sea sediments

Iridium and osmium concentrations were measured in dated deep-sea sediments by neutron activation analysis to attempt to set limits on the influx rate of cosmic matter. Twentyone measurements on five cores from the central Pacific gave Ir and Os contents from 0·06 to 0·4 ppb, with an observed precision of ±15 percent. The Ir and Os contents were correlated with each other: Ir = (1·2 ± 0·2) Os. Both tended to increase with decreasing sedimentation rate. The Ir content can be represented by the expression: Ir ( ppb) = (0·07 ± 0·08) + (0·094 ± 0·047)1/ r s where r s is the sedimentation rate in mm per 1000 years from Th 230 Th 232 ratios. If the first term is interpreted as an average terrestrial component and the second term, as an exclusively cosmic component which is diluted in proportion to the sedimentation rate, an upper limit to the influx rate of cosmic matter may be established on the basis of the average Ir content of some representative meteoritic material. With an assumed Ir content of 0·42 ppm, the value in Type I carbonaceous chondrites, the influx rate for the entire earth becomes (6 ± 3) × 10 4 tons/yr. This value represents an average over the last 10 5 to 10 6 years; the mass range effectively sampled by this method is ~10 −14 to ~10 12 g. A firm upper limit on the influx rate can be obtained by assuming that all the Ir and Os in deep-sea sediments is of cosmic origin. The value obtained is between 0.5 × 10 5 and 1.5 × 10 5 tons/yr. It is more than an order of magnitude lower than other estimates based on the Ni content of deep-sea sediments or particles counts by satellites.