Affiliation:
1. Department of Biology, Georgetown University, Washington, D.C. 20007
Abstract
Studies of Maaløe, Lark, and others with amino acid- and thymine-starved cultures revealed successive steps in the biosynthesis of
Escherichia coli
chromosomes. In this study, the corresponding mechanisms in
Bacillus subtilis
168 were examined. Using a strain requiring both thymine and tryptophan, we found that, 3 hr after the start of amino acid starvation, when the deoxyribonucleic acid (DNA) content of the culture had increased 40 to 50%, DNA synthesis ceased. After 4 to 5 hr, 100% of the cells were immune to thymineless death; their chromosomes had presumably been completed. Immune cultures slowly incorporated
3
H-thymine. Thymine incorporation increased 20-fold 30 min after readdition of amino acids, indicating reinitiation of chromosome synthesis. Simultaneous presence of amino acids and thymine was required for reinitiation. If 5-bromouracil (5-BU) was added instead of thymine, newly replicated DNA segments could be separated by centrifugation in CsCl. Analysis of the CsCl fractions by a transformation assay showed that the order in which the markers were synthesized was
ade-16, thr-5, leu-8, metB5
. Less than half the chromosomes started resynthesis synchronously in 5-BU. Nevertheless, chromosome alignment in the amino acid-starved culture is probably very good: marker frequency analysis of its DNA gives the same normalized frequencies as DNA from “perfectly” aligned spores. Full viability is maintained in the chromosome-arrested culture for 10 hr in thymine-free medium in the absence or presence of amino acids. In the latter condition, protein synthesis proceeds, and the cells filament and become more lysozyme-sensitive. Such cells must be incubated and plated on hypertonic or on slow-growth media; otherwise, they undergo “quasiosmotic” thymineless death. This death is thus apparently not directly attributable to any damage of chromosomal DNA. Further, weakening of the teichoic acid portion of the cell wall is not involved, since
32
P incorporation into teichoic acid is normal. Chloramphenicol prevents quasiosmotic thymineless death and also inhibits
32
P incorporation into teichoic acid. Chromosome-synthesizing cultures suffer thymineless death of two types: quasiosmotic death, and death insusceptible to osmotic rescue.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
30 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献