Deoxyribonucleic Acid Thymine Research Articles

Are Viruses Just Spores?

<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Something amazing happened</b> early in the history of the Earth. Molecules were formed that had the unusual capacity to reproduce. And, not only that, but these molecules reproduced to the limit of the resources available and competed with other, similar, molecules to utilize every available reserve necessary to their growth and reproduction. These molecules were nucleic acids. The earliest nucleic acids were probably ribonucleic acids, strings of phosphate groups, sugars, and nitrogenous bases, known now by the acronym RNA <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . Later, deoxyribonucleic acid (DNA) molecules came to share the available space with RNA. Each of these was similarly constructed as a long-chain molecule, made up of pyrimidine nucleic bases called cytosine (C) and thymine (T), or uracil (U), and the purines adenine (A), and guanine (G). RNA is made of uracil instead of the thymine in DNA. Some RNA and DNA molecules were single-stranded, and some formed as double strands. These molecules formed the genetic bases for all of life on Earth since then.

Loss of deoxyribonucleic acid-thymine during thymine starvation of Escherichia coli.

A substantial loss of deoxyribonucleic acid-thymine occurs during thymine starvation of several thymine auxotrophs derived from Escherichia coli strains B, 15, and K-12.

Evidence for the utilization of preformed purines by rat lymphoid tissues: implication to immunosuppression by 6-thiopurine analogues.

SummaryPortal occlusion selectively inhibits the in vivo incorporation of [14C]formate into the purines of deoxyribonucleic acid isolated from rat lymph nodes and thymus compared with incorporation into deoxyribonucleic acid thymine. Incorporation of formate into deoxyribonucleic acid purines is also low in perfused submandibular lymph nodes and in lymph nodes incubated in vitro. A similar depression of formate incorporation into lymphoid tissue deoxyribonucleic acid purines is obtained by treatment with the immuno‐ suppressive drugs azathioprine and 9‐butylazathioprine.

A radioautographic study of the utilization of deoxycytidine for the formation of deoxyribonucleic acid-thymine in lymphocytes.

A radioautographic study of the utilization of deoxycytidine for the formation of deoxyribonucleic acid-thymine in lymphocytes.

A novel origin of some deoxyribonucleic acid thymine and its nonrandom distribution.

A novel origin of some deoxyribonucleic acid thymine and its nonrandom distribution.

Thymine and thymidine uptake by Haemophilus influenzae and the labeling of deoxyribonucleic acid.

The influence of ribo- and deoxyribonucleosides and ribo- and deoxyribonucleotides on the uptake of radiolabeled thymidine and thymine by Haemophilus influenzae during growth was investigated. A nucleoside-degrading enzyme similar to that reported in Escherichia coli was found to break down thymidine unless other nucleosides were present to divert its action. The presence of other nucleosides permitted a nearly quantitative uptake of even low levels of thymidine. This quantitative uptake of thymidine in the presence of an excess of other nucleosides suggests that the uptake mechanism for thymidine is specific in this organism. Under optimal conditions, as much as 50% of the deoxyribonucleic acid (DNA) thymine was derived from exogenous thymidine. Thymine was not taken up by H. influenzae but, in the presence of purine deoxynucleosides, labeled thymine entered the cells, presumably as thymidine. Ribonucleosides or ribonucleotides inhibited thymine conversion to thymidine, but, as noted above, they were degraded by a cellular enzyme. Thus, unless the ribonucleoside level was excessively high, a cell level of growth was reached at which the inhibiting ribonucleoside was broken down and labeled thymine appeared in the cells at an increasing rate. Twenty-five per cent of the DNA thymine of this organism was labeled with exogenous thymine. The information noted above serves as the basis for isotopically labeling the DNA.

Element analysis in labeled DNA by x-ray fluorescence

An x-ray fluorescence method has been developed which allows for the determination of the degree of replacement of thymine in deoxyribonucleic acid (DNA) by the halogenated uracils, 5-bromouracil, 5-iodouracil and 5-chlorouracil, as well as the sulfur-containing analogs, thioguanine (replacing guanine) and 6-mercaptopurine (replacing adenine). In this method the ratio of the number of halogen (or sulfur) to phosphorus atoms is measured for determination of the degree of replacement. This ratio is obtained dispersively without concern for interline interferences due to elemental impurities in the DNA. The more sensitive nondispersive analytical approach is also used in this system for the determination of bromouracil and iodouracil replacement for isolated DNA material of extreme purity. Under our optimum instrumental conditions, the dispersive approach gives an expected relative counting error for the determination of the Br: P ratio in 10 μg samples of DNA containing 0.5% Br by dry weight (equivalent to about 1% replacement) of 8% for a 10 min integration time. An actual precision measurement on 10 μg samples of DNA with a bromine content of 0.8% dry weight gave a relative standard deviation of 3.7% for the Br: P ratio in a 20 min integration time. Precision analysis on 2 μg samples of Br containing DNA shows the experimental error is less than 1.3 times the expected counting statistical error (see “Results”). The precision in the determination of the Br: P ratio on 2 μg samples of DNA was found to remain practically unchanged with the addition of 8 μg of nonphosphorus containing “impurities,” and the measure of the ratio upon the addition of 80% impurities shows a variation of close to 6% for DNA samples containing about 3% Br by dry weight. The expected error in replacement determinations depends on the amount of replacement. For example, maximal replacement in the order of 0.6% of guanine by TG in Escherichia coli B r ( E. coli B r ) has been reported (13). This is about 100 times less than the maximal replacement of thymine by BU reported for E. coli 15T − and HeLa cells. The statistical counting error in the determination of TG replacement would be greater than 10%, for reasonable integration times, if the degree of replacement to be measured is 0.6% or less. It would also be difficult to determine if the analog is actually incorporated or is present as a nonincorporated impurity at these low levels of replacement.

Effects of Incorporation of Iododeoxyuridine on Escherichia coli

A VARIETY of base analogues which are incorporated into deoxyribonucleic acid (DNA) affect the growth of mammalian cells, bacteria, plant and animal viruses. It has been shown1,2 that thymine substitution by halogenated analogues is higher in thymine-less than in wild bacterial strains. To increase the incorporation in wild-strains, inhibitors of thymidylic acid synthesis were used (aminopterin or sulphanilamide). The substitution of the natural base by the brominated analogue produces some physiological and genetical effects. It was demonstrated3 that bacteria labelled with bromouracil are highly sensitive to ultra-violet irradiation. In some cases the replacement of thymine in DNA produced a significant increase of the frequency of mutations at specific locations of phages T4 or T2 (refs. 4 and 5) or in Salmonella typhimurium at the tryptophan D locus6. In contrast to the brominated analogues, the iodinated analogues of thymine were not thoroughly examined until now.

Severe Distortion by 5-Bromouracil of the Sequence Characteristics of a Bacterial Deoxyribonucleic Acid

THE statement is often encountered in the literature that one or another purine or pyrimidine analogue, not found in the cell normally, can, when it is incorporated into a deoxy- or ribo-nucleic acid, partly replace one of the natural nucleic acid constituents. For example, 5-bromouracil is said to replace some of the thymine in deoxyribonucleic acid, or 5-fluorouracil some of the uracil of ribonucleic acid ; and this view is even applied to minor constituents occurring in Nature, 5-methylcytosine replacing some of the cytosine, pseudouridine some of the uridine. Such statements are derived, implicitly, from the complementariness principles formulated in this laboratory for deoxyribonucleic acid1 and ribonucleic acid2. But what actually is meant by replacement ? If, as is the case, the molar sum of the 6-aminopyrimidines cytosine and 5-methylcytosine equals the molar concentration of the 6-ketopurine guanine in the deoxyribonucleic acid of rye germ3, does this signify that every cytosine molecule along the polymer chain has an equal chance of being ‘replaced’ by a methylcytosine molecule ? We have recently discussed the evidence for this not being the case3.

The Fluorometric Determination of Thymine in Deoxyribonucleic Acid and Derivatives

The Fluorometric Determination of Thymine in Deoxyribonucleic Acid and Derivatives

A Three-stranded Polyribonucleotide Structure

THE synthetic polymers, polyadenylic acid (A) and polyuridylic acid (U) interact strongly when mixed together in aqueous solution. Evidence for interaction on mixing comes from many observations, including increases in viscosity, sedimentation coefficient and molecular weight and decrease in ultraviolet absorption1. The last phenomenon, referred to as a hypochromic effect, is observed in the reverse fashion for deoxyribonucleic acid (P. Doty, private communication), that is, on thermal disruption of the double chain helical molecule in solution there is a substantial increase (about 30 per cent) in the optical density. This parallel behaviour of deoxyribonucleic acid and the chemically related synthetic complex suggests that their structures may be comparable. Added weight to this view is given by X-ray diffraction pictures2 which show remarkable similarities between naturally occurring deoxyribonucleic acid and a synthetic fibre of polyadenylic acid/polyuridylic acid (AU) drawn from a solution containing equimolar portions of polyadenylic and polyuridylic acids. These facts have led Rich3 to propose that the hydrogen bonding in the polyadenylic acid/polyuridylic acid complex is of the same type as that observed between adenine and thymine in deoxyribonucleic acid.

STUDIES ON A RELATIONSHIP OF URACIL AND CYTOSINE NUCLEOSIDES TO BIOSYNTHESIS OF DEOXYRIBONUCLEIC ACID THYMINE

STUDIES ON A RELATIONSHIP OF URACIL AND CYTOSINE NUCLEOSIDES TO BIOSYNTHESIS OF DEOXYRIBONUCLEIC ACID THYMINE

Lack of differential radiation effect on the incorporation of labelled precursors into deoxyribonucleic acid.

IT has been reported that formate carbon-14 is preferentially taken up into deoxyribonucleic acid thymine by bone marrow cells in vitro 1,2. This has been further confirmed by the ‘thymidine dilution test’. Suspensions of human bone marrow cells were cultured in vitro 3, and the formate carbon-14 uptake was measured on high-resolution autoradiographs using the stripping film method on alcohol-fixed smears from such cultures4. The proportion of labelled cells (‘per cent positive’) was obtained by counting 250 cells, and the average count per cell by grain counts over 50 cells. The error-range of such counts is within ± 10 per cent. It was found that 0.18 mgm./ml. medium thymidine depressed formate carbon-14 uptake by 80 ± 11 per cent (seven experiments), while leaving adenine carbon-14 uptake unaffected (four experiments).

A chromatographic study of hydrolysis in the Feulgen nucleal reaction.

In a study on Feulgen hydrolysis of frozen-dried alcohol-fixed lily anthers, a chromatographic technique was developed to analyze the acid hydrolysate for some of the degradation products of nucleic acid. Hydrolysis was accomplished by 10 per cent perchloric acid at 20 degrees C., and a typical hydrolysis time-Feulgen intensity curve was obtained, with maximum staining occurring at 19 hours. Microphotometric measurements indicated that the amount of stain per nucleus was no different from amount in nuclei fixed and hydrolyzed by more conventional procedures. Uracil-containing material (from ribonucleic acid) was almost completely separated from thymine-containing material (deoxyribonucleic acid) of tissue sections by acid treatment for 1(1/2) hours. Adenine (purines), as the base, was effectively all removed from the deoxyribonucleic acid at the time of optimum hydrolysis. Detectable amounts of thymine-containing material appeared in the hydrolysate shortly after the onset of hydrolysis; and the amount increased rapidly with increased hydrolysis time. At the time of optimum hydrolysis approximately two-thirds of the total deoxyribonucleic acid thymine was lost. The removal of these thymine-containing fragments was linear with respect to time during the first 24 hours and occurred at a relatively high rate. Removal after 24 hours was also linear but was at a markedly lower rate. These results would suggest that two kinds of deoxyribonucleic acid exist in lily anthers; an acid-labile fraction amounting to approximately three-fourths of the total, and an acid-resistant fraction making up the remainder. In the Feulgen procedure much of the labile fraction is lost by the time of optimum hydrolysis and is not stained; most of the stable fraction remains in the tissue and is stained. In light of these findings the use of the Feulgen method as a means of determining cytochemically relative amounts of deoxyribonucleic acid in nuclei by measuring their Feulgen dye content was discussed.