Deoxyribonucleic Acid Homology and Relative Genome Size in Mycoplasma

The deoxyribonucleic acid homologies of Mycoplasma laidlawii type A and type B, M. pulmonis (#47 and #63), and M. hominis were determined by membrane methodology. The homology data revealed a difference in genome size between M. laidlawii type A and type B. This difference also held with stringent conditions of annealing (high temperature). Little or negligible homology was shown to exist between the M. laidlawii strains type A and type B and M. pulmonis strains 47 and 63 and M. hominis. M. hominis showed less than 10% homology to the M. pulmonis and M. laidlawii strains. Neither of the M. laidlawii strains showed more than 2% annealing to the M. pulmonis strains. Reaction rate studies are suggested as a means of demonstrating the phylogenetic relationship between the Mycoplasma and other microorganisms.     

Relationship Between Sporulation-Specific 20S Ribonucleic Acid and Ribosomal Ribonucleic Acid Processing in Saccharomyces cerevisiae

The nature and properties of the 20S ribonucleic acid which accumulates only during the sporulation of Saccharomyces cerevisiae were examined. The 20S ribonucleic acid (RNA) has a base composition considerably different from ribosomal RNA species and is virtually unmethylated. The 20S RNA did, however, exhibit approximately 70% homology with 18S RNA by RNA-deoxyribonucleic acid filter hybridization competitions. The 20S RNA showed a hybridization saturation plateau level 30 to 40% higher than 18S, consistent with measurements of the size difference in polyacrylamide gels. Pulse-chase experiments in the presence and absence of cycloheximide indicate that the 20S RNA has a presumptive relationship to the 20S ribosomal RNA precursor normally observed only in short pulse-labeling in vegetative cells.     

Variability in Complementarity for Chloroplastic and Cytoplasmic Ribosomal Ribonucleic Acid among Plant Nuclear Deoxyribonucleic Acids

The nuclear DNAs from a number of angiosperm species were tested for hybridization to the RNAs contained in 70 S (chloroplastic) and 80 S (cytoplasmic) ribosomes. All of the DNAs contained regions complementary to RNAs from chloroplastic as well as cytoplasmic ribosomes. DNAs from closely related plants varied widely in their proportion of coding for these RNAs. About 0.15% of the DNAs from a number of different species of Nicotiana were found to be complementary to the RNAs of each kind of ribosome; however, DNAs from some other members of this genus had more than three times this proportion of coding for ribosomal RNAs. These and other data suggest that hybridization percentage for ribosomal RNA is not a familial or generic characteristic.     

Ribonucleic Acid-Dependent Deoxyribonucleic Acid Polymerase in Visna Virus

A ribonucleic acid-dependent deoxyribonucleic acid polymerase was found in virions of visna virus. The enzyme product was resistant to ribonuclease and alkaline hydrolysis but susceptible to the digestion of deoxyribonuclease.     

Role of Ribonucleic Acid Synthesis in Replication of Deoxyribonucleic Acid

An experiment previously interpreted to show a ribonucleic acid requirement for propagation of deoxyribonucleic replication is reexamined and the earlier interpretation is shown to be incorrect.     

Gene Dosage for 5S Ribosomal Ribonucleic Acid in Escherichia coli and Bacillus megaterium

The number of gene copies for 5S ribosomal ribonucleic acid (rRNA), relative to that for 16 and 23S rRNA, has been determined by deoxyribonucleic acid (DNA)-RNA hybridization for Escherichia coli and Bacillus megaterium. In both cases, the number of 5S rRNA genes equals the number of 16 or 23S rRNA genes. Rapid procedures for preparing extremely highly purified DNA suitable for DNA-RNA hybridization experiments and chemically pure 5S rRNA are described.     

Ribosomal Precursors and Ribonucleic Acid Synthesis in Escherichia coli

Ribosomes and immature ribonucleoprotein particles were isolated from extracts of log-phase cells grown under various conditions. Quantitative measurements were made to determine the relative amounts of immature particles present in the extracts. The results indicate that the steady-state level of ribosomal precursors accounted for essentially a constant fraction of the total ribonucleic acid (RNA) of the cells. For cells with RNA-protein ratios between 0.43 and 0.65, about 1.6% of the total RNA occurred as immature ribonucleoprotein particles. Further, increased levels of immature particles were shown to be correlated with a reduced rate of RNA synthesis in cells recovering from chloramphenicol inhibition. The reduction was found to vary directly with the duration of pretreatment in chloramphenicol and, consequently, with the level of immature particles present in the cells.     

Control of Deoxyribonucleic Acid and Ribonucleic Acid Synthesis in Pyrimidine-Limited Escherichia coli

The effects of pyrimidine limitation on chromosome replication and the control of ribosomal and transfer ribonucleic acid syntheses were investigated. Chromosome replication was studied by autoradiography of (3)H-thymine pulse-labeled cells. Pyrimidine limitation did not affect the fraction of cells incorporating radioactive thymine during a short pulse, indicating that when growth is limited by the supply of pyrimidine, the time required for chromosome duplication increases in proportion to the time required for cell duplication. Control of ribosomal RNA and transfer RNA syntheses was examined by chromatographing cell extracts on methylated albumin kieselguhr columns. When growth was controlled by carbon-nitrogen limitation, the ratio of tRNA to total RNA remained roughly constant at growth rates above 0.5 doublings per hour. During pyrimidine limitation, however, the control of rRNA synthesis was apparently dissociated from the control of tRNA synthesis: the ratio of tRNA to total RNA increased as the growth rate decreased.     

Ribonucleic Acid from Aerobically and Anaerobically Grown Rhodopseudomonas spheroides: Comparison by Hybridization to Chromosomal and Satellite Deoxyribonucleic Acid

Ribonucleic acid (RNA) species from aerobically and anaerobically grown Rhodopseudomonas spheroides were compared via hybridization to deoxyribonucleic acid (DNA). Both long-labeled and stable RNA bound to chromosomal DNA to the same extent, regardless of derivation. About 4% of the chromosomal DNA hybridized with total cell RNA and about 0.08% with stable RNA. About 4% of the mixed satellite DNA could be hybridized to total cell RNA from aerobic or anaerobic cultures, whereas essentially no stable RNA formed a hybrid with this DNA. Hybridization competition experiments with aerobic and anaerobic pulse-labeled RNA and chromosomal or satellite DNA demonstrated that no qualitative differences existed between the RNA species. It is concluded that identical species of RNA in the same relative amounts are synthesized by R. spheroides during aerobic or anaerobic growth on the same medium.     

Deoxyribonucleic Acid, Ribonucleic Acid, Protein and Uncombined Amino Acid Content of Legume Seeds During Embryogeny

The nucleic acid, protein and uncombined amino acid contentof seeds of soya-bean (Glycine max L. Merr.), garden pea (Pisumsativum L.), kidney bean (Phaseolus vulgaris L.) and peanut(Arachis hypogaea L.) were measured at various times duringseed formation in an effort to understand why the soya-beanhas nearly twice as much protein as the other legume seeds.In all these species the concentration of deoxyribonucleic acid,ribonucleic acid and uncombined amino acids decreased duringseed formation. The protein level of kidney bean was relativelyconstant during development whereas the protein levels of pea,peanut and soya-bean increased during development. The proteincontent of the soya-bean increased throughout development whereasthe protein increase in peanut took place early and that inpea took place later in development. The ratio of protein toribonucleic acid was highest in peanut, less in soya-bean, andlowest in pea and kidney bean. Similarly, the ratio of proteinto deoxyribonucleic acid was higher in kidney bean than in soya-bean.Soya-beans had a lower amino acid content than any of the otherseeds at all stages of development. These results indicate thatneither total deoxyribonucleic acid, ribonucleic acid nor uncombinedamino acid content is responsible for the higher protein contentof soya-beans.     

Ribosome Development and the Methylation of Ribosomal Ribonucleic Acid

Immature ribonucleoprotein particles accumulate in amino acid-starved cells of a relaxed mutant of Escherichia coli. The ribonucleic acid (RNA) of these particles is nonmethylated in cells starved for methionine. However, in bacteria starved for arginine, lysine, or histidine, the RNA of these particles is one-half methylated. The relationship of submethylation to a structural alteration in the same RNA was studied. The results of kinetic studies showed that submethylation and the structural transition are not causally related, since they are described by different rate constants. Moreover, it was possible to accumulate fully methylated immature-particle RNA that possessed the sedimentation and chromatographic properties of nonmethylated RNA. It was concluded that, during the normal course of ribosome development, methylation of ribosomal RNA is completed prior to the final maturation steps.     

Ribonucleic Acid, Deoxyribonucleic Acid, and Protein Content of Cells of Different Ages of Mycobacterium tuberculosis and the Relationship to Immunogenicity

The amount of ribonucleic acid (RNA), protein, and deoxyribonucleic acid (DNA) was determined in pellicle cultures of different ages of the H37Ra strain of Mycobacterium tuberculosis, grown on a synthetic medium. We found that the highest content of RNA and protein was present in 2-week-old cultures, indicating that these cells were in the logarithmic phase of growth. DNA content was highest at 1 and 2 weeks. The amount of all three compounds then decreased about 50% during the following 6 weeks. Two-week-old cells should therefore be used for preparation of the immunogenic ribosomal fraction. The optimal concentration of zinc chloride increased RNA and protein synthesis, and also improved the appearance of the pellicle growth. Two-week-old cells, which contained the largest amount of RNA and protein, immunized mice significantly better than older cells. Since protein and DNA are not involved in the production of immunity, a correlation could be made between amount of RNA and the capacity of viable H37Ra cells to immunize mice. The immunizing capacity of these cells was not affected by ribonuclease, probably because the ribonuclease did not penetrate into the whole cells.     

Synthesis of Replicative Form Deoxyribonucleic Acid and Messenger Ribonucleic Acid by Gene IV Mutants of Bacteriophage S13

Gene IV mutants of bacteriophage S13 are known to be blocked in infectious replicative form (RF) DNA synthesis, producing only a small fraction of the RF formed by wild-type phage. This investigation shows that gene IV mutants form only parental RF and are blocked in the synthesis of any progeny RF, either infectious or noninfectious. This was determined by density labeling of RF in cells treated with mitomycin C to suppress host deoxyribonucleic acid (DNA) synthesis. RF synthesis was also studied in untreated cells, using methylated albumin columns to separate RF from host DNA. In this case it was also found that synthesis of progeny RF by gene IV mutants is negligible. It has been found by DNA-ribonucleic acid (RNA) hybridization experiments that gene IV mutants form at least as much or more messenger RNA than wild-type phage. Therefore, parental RF alone can form messenger RNA in appreciable amounts.     

Inhibition of Bacterial Conjugation by Ribonucleic Acid and Deoxyribonucleic Acid Male-Specific Bacteriophages

Both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) male-specific phages, with an F-specific host range, inhibited the bacterial mating process of Escherichia coli. DNA phages prevented the formation of mating pairs but had no effect on mating pairs once they were formed. A step in RNA phage infection, prior to RNA penetration, prevented the formation of mating pairs and, in addition, prevented a fraction of existing mating pairs from completing the mating process. These findings are compatible with the hypothesis that donor cells have a single surface structure involved in both conjugation and male-phage adsorption and that this element is the F pilus.     

禾本科植物基因组大小与种子特性的相关性分析

在检索植物C值数据库和种子数据信息库的基础上,对禾本科282种植物的基因组参数（倍性、染色体数、C值、GS值和平均每条染色体DNA含量）和种子特性（千粒重、含油量和蛋白含量）进行了统计分析。分析结果表明,禾本科植物C值在0.35～19.7 pg,大多位于1.6～3.2 pg之间,呈偏正态分布,种子千粒重在0.05～252 g,绝大多数位于0.05～20.0 g,呈偏态分布,二者平均值分别为4.14 pg和7.1 g。随着染色体倍性增加,C值在二倍体到八倍体之间显著增加,而GS值和平均每染色体DNA含量在二倍体到六倍体之间显著下降（p<0.05)。雀麦属和羊茅属随着倍性增加,C值显著增加,表现与禾本科相似的变化规律,GS值下降却不明显。相关性分析表明,禾本科植物C值与倍性、染色体数、GS值及平均每条染色体DNA含量均呈极显著正相关（p<0.01),与种子千粒重无相关性。GS值与染色体数、倍性呈极显著负相关,而与千粒重呈极显著正相关。C值与种子含油量呈显著负相关,但与种子蛋白含量之间无相关性。以上结果表明,禾本科植物在系统演化和进化过程中,主要通过倍性和染色体的增加来增大C值,可能通过某种删除或丢失机制来降低GS值,从而保持较高的适应环境能力和进化速率。     

Intraspecific Variation of Ribosomal Gene Redundancy in ZEA MAYS

Ribosomal genes in eukaryotes are highly redundant. Considerable variation in the level of redundancy among species, especially in higher plants, has been reported; but except for deletion and duplication mutants, it is generally accepted that intraspecific variability in redundancy level is small. We have examined the level of redundancy in several lines of maize by DNA-rRNA saturation hybridization. The amount of nuclear DNA which hybridizes with rRNA in the ten lines examined varied from 0.24% to 0.50%. The number of rRNA genes per diploid genome thus ranges from 1.12 x 10⁴ to 2.32 x 10⁴. Results also indicate that the level of redundancy is genetically transmitted.     

Relationships Among Deoxyribonucleic Acid, Ribonucleic Acid, and Specific Transfer Ribonucleic Acids in Escherichia coli 15T− at Various Growth Rates

The levels of macromolecules in Escherichia coli 15T(-) growing in broth, glucose, succinate, and acetate media were determined to compare relationships among deoxyribonucleic acid (DNA), ribosomal ribonucleic acid (rRNA), transfer RNA (tRNA), and protein in cells at different growth rates. DNA and protein increased in relative amounts with decreasing growth rate; relative amounts of rRNA and tRNA decreased, tRNA making up a slightly larger proportion of RNA. For several amino acid-specific tRNAs studied, acceptor capacities per unit of DNA increased with increasing growth rate. The syntheses of tRNA and rRNA are regulated by similar, yet different, mechanisms. Chromatographic examination on columns of benzoylated diethylaminoethyl-cellulose of isoaccepting tRNAs for arginine, leucine, lysine, methionine, phenylalanine, serine, and valine did not reveal differences in the isoaccepting profiles for rapidly (broth culture) and slowly growing (acetate culture) cells. Therefore, isoacceptors for individual amino acids appear to be regulated as a group. Lower efficiencies of ribosomal function in protein synthesis can be explained, in part, by a low ratio of tRNA to the number of ribosomes available and by a decreasing concentration of tRNA with decreasing growth rate. Data on the tRNAs specific for seven amino acids indicate that the decreasing concentration of tRNA is a general event rather than a severe limitation of any one tRNA or isoaccepting tRNA.     

Comparative Study of Ribosomal Ribonucleic Acid Cistrons in Enterobacteria and Myxobacteria

Deoxyribonucleic acid (DNA)-ribonucleic acid (RNA) hybrids are formed by Escherichia coli 16S or 23S ribosomal RNA or pulse-labeled RNA with the DNA of various species of the Enterobacteriaceae. The relative extent of hybrid formation is always greater for ribosomal RNA. These DNA-RNA hybrids have been further characterized by their stability to increasing temperature, and, in every case, the stability of pulse-labeled RNA hybrids was lower than that of the corresponding ribosomal RNA hybrids, although 16S and 23S ribosomal RNA hybrids had very similar stabilities. Therefore, ribosomal RNA showed a greater degree of apparent conservation in base sequence than pulse-labeled or messenger RNA both in the extent of cross-reaction and in the stability of hybrid structures. Similar results were obtained with Myxococcus xanthus RNA. Since in this case the base composition of the pulse-labeled or messenger RNA is richer in guanine plus cytosine than ribosomal RNA, the higher cross-reaction of ribosomal RNA is more readily attributable to conservation of base sequence in these cistrons than to its base composition. Thus, the base sequence of ribosomal RNA cistrons of bacilli, enteric bacteria, and myxobacteria is conserved relative to those of the rest of the genomes. This conservation is, however, not absolute since the stability of heterologous ribosomal RNA hybrids is always lower than that of homologous hybrids.