Sporadic Formation Research Articles

Non-Shine-Dalgarno Initiators of Translation Selected from Combinatorial DNA Libraries

In a search for non-Shine-Dalgarno (non-SD) translational initiators, two combinatorial expression libraries (denoted R₁ and R₂) were constructed containing randomized decanucleotide regions placed at either 6 (R₁) or 11 (R₂) nucleotides upstream of a modified chloramphenicol acetyltransferase (CAT) gene. To prevent sporadic formation of SD-like sequences the content of G in the randomized region was restricted to 3% only. The two libraries were transformed in Escherichia coli cells and screened for chloramphenicol (Cm) resistance. More than 50 clones capable of tolerating Cm concentrations from 50 µg/ml to more than 800 µg/ml were selected. With few exceptions only, the non-SD sequences found in the Cm-resistant clones did not show any significant homology with other known non-SD initiators or enhancers of translation. Statistical (χ²) analysis of the distribution of nucleotides in the new non-SD translational initiators showed a different pattern from that of the conventional SD sequences. In few of the clones the yield of CAT exceeded that of the referent (SD-containing) construct. The most productive clones carried the decanucleotides ATTTACCTCC, CCAATCTAC, TTCAATATTT, and TATTCCCCCA, and the corresponding yield of CAT obtained with them was 2.70, 2.06, 2.12 and 1.32 times, respectively, higher than that of the SD-bearing construct.

DETERMINATION OF LOCAL MECHANICAL PROPERTIES OF α- AND β-PP BY MEANS OF MICROHARDNESS MEASUREMENTS

A study has been made of the microhardness properties of α- and β-spherulites in unnucleated isotactic polypropylenes. For this purpose, a high-molecular weight homopolymer and a random copolymer with 4 mol% ethylene were used. Both materials tend to sporadic formation of β spherulites. The α- and β-spherulites were differentiated under an optical microscope, allowing the microhardness measurements of individual spherulites of each crystallographic form. Different crystallization and annealing temperatures were used. Independent of these conditions, microhardness and modulus determined by indentation testing are lower for the β-phase in both materials. Increasing crystallization temperature and annealing lead to an increasing hardness and modulus in both phases. However, an effective annealing effect takes place only at short times and elevated temperatures The increasing of microhardness and modulus is correlated with an increasing in lamellae thicknesses.

Somatic PKD2 mutations in individual kidney and liver cysts support a "two-hit" model of cystogenesis in type 2 autosomal dominant polycystic kidney disease.

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic formation of renal and extrarenal cysts. Recent documentation of somatic PKD1 mutations in cystic epithelia of patients with germ-line PKD1 mutations suggests a "two-hit" model for cystogenesis in type 1 ADPKD. This study tests whether the same mechanism for cystogenesis might also occur in type 2 ADPKD. Genomic DNA was obtained from 54 kidney and liver cysts from three patients with known germ-line PKD2 mutations, using procedures that minimize contamination of cells from noncystic tissue. Using intragenic and microsatellite markers, these cyst samples were screened for loss of heterozygosity. The same samples were also screened for somatic mutations in five of the 15 exons in PKD2 by single-stranded conformational polymorphism analysis. Loss of heterozygosity was found in five cysts, and unique intragenic mutations were found in seven other cysts. In 11 of these 12 cysts, it was also determined that the somatic mutation occurred nonrandomly in the copy of PKD2 inherited from the unaffected parent. These findings support the "two-hit" model as a unified mechanism for cystogenesis in ADPKD. In this model, the requirement of a somatic mutation as the rate-limiting step for individual cyst formation has potential therapeutic implications.

Emergence of template-and-sequence-directed (TSD) syntheses: II. A computer simulation model.

The initiation of the bio-geochemical scenario described in Part I serves in the present work as the basis for computer modeling, where the central process of the simulation algorithm. i.e., peptide-catalyzed oligomeric growth, is based on mass action equations. The computer model starts with a minimal system in which catalyzed growth processes of proto-RNA templates and small peptides take place, starting from their building blocks. The emerging populations of random oligomers also include a very small fraction of proto-tRNAs and a small fraction of catalytic peptides. Using simplifying assumptions regarding catalyzed proto-RNA template-replication, as well as selectivity of certain molecules and processes, the proportion of proto-tRNA in the proto-RNA molecular population increases rapidly; it is followed by TSD peptide synthesis, based on an ad hoc genetic code and specific peptide catalysts allocated for this synthesis. Consequently, a feedback system is initiated in which TSD peptides involved in the relevant catalytic reactions of the TSD syntheses also start to accumulate. The initial sporadic formation of TSD peptides is thus replaced gradually by cycles of positive feedback and autocatalysis characterized by accumulation of catalytic peptides and Proto-tRNAs and TSD-Reaction-Takeover. The model system which can be considered a 'toy model' can synthesize its templates and catalysts under a wide range of reaction parameters and initial concentrations, thus demonstrating a robustness which is essential for molecular evolution processes. The critical stage of the buildup of a molecular mechanism for the initiation of a minimal TSD reaction cycle has thus been described; because of the centrality of TSD reaction cycles in biology, it is assumed to be central also in the origin of life processes.

Measurements of superadiabatic lapse rates in the middle atmosphere

A large power‐aperture product Rayleigh‐scatter lidar system has been successfully built and over 175 nights of middle atmosphere temperature measurements have been obtained. The high signal‐to‐noise ratio of these measurements allows the stability of the air in the upper stratosphere and mesosphere to be determined. A detailed methodology has been developed to attempt to differentiate between lapse rate variations due to photon counting errors and actual geophysical variations. On nights when the geophysical variations are large compared to the photon counting errors, regions of convective stability and instability can be determined at a reasonably high confidence level. Both statistics of the layers and an “image” of the layers is presented for the night of May 31, 1996. The measured percentage of unstable layers is in agreement with the predictions of Hines (1991), as is the apparently sporadic formation and distribution of the unstable regions.

ECOLOGICAL AND GENETIC ASSOCIATIONS IN AN IRIS HYBRID ZONE.

Chloroplast DNA (cpDNA) markers and 12 nuclear (random amplified polymorphic DNA, or RAPD) markers were used to examine the distribution of genetic variation among individuals and the genetic and ecological associations in a hybrid iris population. Plants in the population occurred at various distances from the edge of a bayou in a relatively undisturbed mixed hardwood forest and in an adjacent pasture dominated by herbaceous perennials with interspersed oak and cypress trees. The majority of plants sampled possessed combinations of markers from the different Iris species. Genetic markers diagnostic for Iris fulva and I. brevicaulis occurred at high frequencies, whereas markers diagnostic for I. hexagona were infrequent. For the majority of the nuclear markers, significant levels of cytonuclear disequilibria existed because of intraspecific associations among the markers in both the pasture and the forest. The distribution of nuclear markers among individuals was bimodal; intermediate genotypes were absent and the majority of RAPD markers were associated with their intraspecific cpDNA haplotypes. Strong intraspecific associations existed among RAPD markers in the forest, but associations tended to be weaker in the pasture area. Ecological correlations were detected for all but one of the I. fulva and I. brevicaulis RAPD markers. The ecological associations of hybrids similar to I. brevicaulis resembled associations of I. brevicaulis parental genotypes, suggesting that these hybrid genotypes may be relatively fit in the same habitats. The hybrids similar to I. fulva, however, were distributed in habitats that were unique relative to the parental species. The patterns of genetic and environmental associations along with other available data suggest that (1) only advanced generation hybrids were present in the population; (2) formation of F1 hybrids among Louisiana irises is rare, leading to sporadic formation of hybrid populations; and (3) selection and assortative mating have contributed to the formation of hybrid genotypes that tend to be similar to parental genotypes. The patterns of ecological and genetic associations detected in this population suggest that assortative mating and environmental and viability selection are important in the structuring and maintenance of this hybrid zone.

Morphology and Meiotic Behavior of Three Dendrobium Amphidiploids and Their Diploid Counterparts

Floral characteristics, meiotic behavior, and sporad formation were compared in three Dendrobium tetraploids (amphidiploids) and their diploid counterparts. Amphidiploid flowers were larger than those of diploids. Diploid meiotic behavior varied; mean configurations at Metaphase I ranged from 14.3 bivalents and 9.4 univalents to 18.9 bivalents and 0.2 univalents. In amphidiploids, nearly all cells had 38 bivalents. Sporad formation also varied; diploids had 36% to 70% tetrads and amphidiploids had 97% to 100% tetrads. Preferential pairing and small chromosome size may promote bivalent formation in amphidiploids.

Putative tumor suppressor gene on chromosome 11 is important in sporadic endocrine tumor formation

Putative tumor suppressor gene on chromosome 11 is important in sporadic endocrine tumor formation

Distribution function of the sporadic E-layer screening frequency

The distribution function of the sporadic E-layer screening frequency is derived using the techniques of mathematical statistics and the physical theory of sporadic E-layer formation. The function is compared to the empirical distribution functions known from literature. The best correlation of the obtained distribution and experimental data is shown.

An advanced generation of Aranda orchids

Aranda orchids are a group of artificially bred intergeneric hybrids between member species (2n = 38) of two natural genera, Vanda and Arachnis, of Orchidaceae. Nine second generation Aranda cultivars were selected for analysis of somatic chromosome numbers, meiotic behaviour, and sporad formation. Eight of the cultivars were derived from Aranda × Vanda crosses and one from an Aranda × Aranda cross. Chromosome counts of their root tip cells showed that eight of them contained 2n = 3x = 57 chromosomes each, presumably resulting from unreduced eggs of the Aranda parent fertilized by haploid Vanda pollen. The ninth revealed 2n = 2x = 38 chromosomes. Pollen mother cells of eight of the cultivars (2n = 3x = 57) commonly formed more than 10 bivalents, presumably between homologous Vanda chromosomes, as well as many univalents, mainly of Arachnis chromosomes. Only 8–10 bivalents were observed in pollen mother cells of the ninth cultivar (2n = 2x = 38). All the cultivars formed a range of dyads containing unreduced microspores. Two mechanisms are proposed for the origin of these dyad sporads.Key words: Aranda orchids, intergeneric hybrids, cytology.

Regional variations in degradation and density of Martian craters

Martian craters visible on Mariner 6 and 7 imagery show a spectrum of topographic types from very fresh to highly degraded. A method of numerical scoring of rim, wall, and floor is proposed to yield a degradation number to classify each crater. Plots of degradation class vs density of large craters are similar for all four regions studied, whereas similar plots for small craters show marked differences between regions. The data suggest general continuity of crater formation and degradation, along with locally sporadic formation and/or degradation of the smallest craters classified. Deucalionis Regio, with an excess of fresh, small craters, experienced an episode of small crater formation (or nondegradation) most recently; Margaritifer Sinus was similarly disturbed at some more remote time. Meridiani Sinus and Hellespontus-Noachis show little or no sign of excess fresh, small craters.

Low stratus at Embakasi Airport Nairobi

The relatively frequent occurrence of low cloud in the area of Embakasi Airport near Nairobi (Kenya) is a great hazard particularly to aircraft without automatic landing device. The desire was therefore that the flight direction and control staff receive early and reliable information of low cloud from the meteorologist. The great difficulty is evident from the fact that low stratus can form and also disappear very suddenly. Considerable and sudden local and temporal variations prevent the meteorologist from an exact forecast of the phenomenon. The statistical results worked out from more than five years of observations should provide a means to tackle the problem, but they appear not to be sufficient unless the actual state of the atmosphere in its lowest 200 metres near the airfield is taken into account as an additional aid for the forecast. Radiosounding from a site to the northeast and below the level of the airfield would be of more use than that from Dagoretti which lies downstream and at a greater altitude. This suggestion had been made when the difficulties with the low cloud forecast became obvious. In the months with predominant low cloud during the night and morning hours the meteorologist will be prepared to foresee the occurrence of low cloud but must be alert in the months with only sporadic formation. A forecast based on merely statistic results is then not sufficiently reliable, if not impossible.

Cyclic variations of the initial height of the sporadicE-layer at middle geographical latitudes

The variations of the initialh′ Es height are investigated in the solar cycle 1957–1968, deriving the regressive dependency:h′ Es=121.4−6·10−2R referring to the median monthly values at a solar zenith angle ξ=75°. The similar variations ofh′Es(R) during the day and night are interpreted as a domination of the sporadic layer formation from a redistribution of the day-time ionization and secondary participation of nightly ionizing sources. The analogous cyclich′ Es andh′ E variations confirm this conclusion while the seasonal variations in the state of the sporadic layer show outlined dynamical effects. The comparatively not big cyclic variation in the spatial state of theE-region are considered to confirm the predominating ionizing action of the ultraviolet range λλ(933–1038 A) in the lower part of theE-region, while the soft X-radiation influences mainly the near maximum part of this region.

A CYTOGENETIC ANALYSIS OF THREE ASYNAPTIC MUTANTS INBRASSICA CAMPESTRISL.

Genetic data on three asynaptic mutants showed that all are monogenically controlled by recessive genes. Differences in cytological abnormalities suggested that each mutant was controlled by a separate gene. The symbol, as, is proposed for these characters with the designations, as, as2, and as3.The degree of asynapsis varied from complete failure of pairing in two of the mutants to partial asynapsis in the third. Other aberrations, such as chromosome fragmentation, lagging, attenuated univalents, micronuclei, restitution nuclei, and aberrant sporad formation were observed. The value of these asynaptics in breeding and cytogenetic research is discussed.

CHEMICAL INDUCTION OF HAPLOID FRUITING BODIES IN Schizophyllum commune

The formation of fruiting bodies in the higher Basidiomycetes is the most dramatic expression of differentiation and morphogenesis that can be found among the fungi. Although fruiting is normally a property of dikaryotic mycelia,l 2 which in heterothallic species are formed from the interaction of compatible homokaryotic strains,3 it is by no means restricted to the dikaryophase. The extensive literature on the physiology, development, and genetics of Basidiomycetes contains numerous references to the sporadic formation of normal or subnormal fruiting structures on the haploid mycelia of a number of species.l' 4-9 Among the principal conditions that have been reported to trigger fruiting body development in haploid mycelia are mycelial aging,' nutrient exhaustion,s and mechanical injury.' Occasional reports have also indicated that chemical substances, e.g., the metabolic products of unrelated species of microorganisms, can initiate the process of fruiting.' 11 Moreover, the specific occurrence of haploid fruiting in individual strains of any one species and its absence in other such strains have implicated an important genetic component in the control of the process.l, 7 9 In all these cases, to be sure, full expression of the haploid fruiting response has required appropriate environmental conditions of growth, e.g., low CO2 tension, adequate illumination, suitable limits of pH and temperature, and an adequate supply of essential nutrients. The present study originated from the chance observation of an intermycelial reaction between a haploid strain of the Basidiomycete Schizophyllum commune and an imperfect fungus, Hormodendrum cladosporioides, which resulted in the induction of haploid fruiting bodies in the former. The present communication reports (a) the demonstration of a fruiting-inducing substance (FIS) in cell-free extracts of the isolate of Hormodendrum and the presence of materials with similar activity in certain stages of S. commune itself; (b) the physiological factors which affect the expression of FIS-induced fruiting; and (c) the preliminary attempts to characterize the inducing substance. Materials and Methods.-The mycelia of S. commune used for the major portion of this study were three homokaryons, isogenized, with the exception of their mating-type factors, by ten generations of backcrossing with strain 699, and heterokaryons derived from their intermating. In addition to this isogenic series, haploid strains of diverse origin and mating type were used for a number of tests. Some of these strains were obtained from Professor John R. Raper of Harvard University, whereas other strains were newly isolated from fruiting bodies collected in the vicinity of Bloomington, Indiana. The isolate of H. cladosporioides employed throughout this study was obtained as a laboratory contaminant and maintained on Difco's Cantino-PYG medium; this medium permitted little conidiation of the fungus and allowed maximal production of active FIS. All fruiting assays, test matings, and spore isolations were carried out on a medium (MM) that contained 20 gm glucose, 1.5 gm asparagine, 1.0 gm K2HP04, 0.46 gm KH2P04, 0.5 gnm MgS04-7H20, 120 1 g thiamine hydrochloride, and 17 gm agar per liter of dis

VEGETATIVE AND REPRODUCTIVE GROWTH OF BLACK SPRUCE (PICEA MARIANA (MILL.) BSP.) AT CHALK RIVER, ONTARIO, CANADA

Apical growth of the leader and lateral branches, as well as radial increment at the top and bottom of the trunk, were studied in two black spruce trees during 1960–63. The study complemented that of the developmental anatomy of shoot tips from adjacent trees during the period 1955–62. Time of initiation of apical growth varied from the third week of May in 1960, 1962, and 1963 to early June in 1961. The termination period of apical growth extended from early July in the lower branches, until about 2 weeks later in the upper branches and leader. Radial increment in the trunk started at about the same time as bud swelling and continued into August. A temporary mid-summer cessation of radial increment occurred at the top of the tree in two consecutive years. The response to artificially induced short and long days from May to August in 12-year-old saplings indicated that initiation of apical growth is not affected by photoperiod. Short days were associated with a reduction in apical extension, needle length, and growth period.Reproductive buds could be recognized by early August, but the formation of ovuliferous scales or pollen sacs did not occur until several weeks later. The male cones differentiated about 1 week before the female ones. The consistent production of flower buds in black spruce compared to the sporadic formation in white spruce is partly attributed to the difference in time of initiation of apical growth. In black spruce the development of buds occurs about 2 weeks later, usually during a warmer part of the summer when conditions are considered more conducive to reproductive growth.