DNA synthesis in prokaryotes: replication

Temporal sequence of events during the initiation process in Escherichia coli deoxyribonucleic acid replication: roles of the dnaA and dnaC gene products and ribonucleic acid polymerase

Three thermosensitive deoxyribonucleic acid (DNA) initiation mutants of Escherichia coli exposed to the restrictive temperature for one to two generations were examined for the ability to reinitiate DNA replication after returning to the permissive temperature in the presence of rifampin, chloramphenicol, or nalidixic acid. Reinitiation in the dnaA mutant was inhibited by rifampin but not by chloramphenicol, whereas renitiation was not inhibited by rifampin but not by chloramphenicol, whereas reinitiation was not inhibited in two dnaC mutants by either rifampin or chloramphenicol. To observe the rifampin inhibition, the antibiotic must be added at least 10 min before return to the permissive temperature. The rifampin inhibition of reinitiation was not observed when a rifampin-resistant ribonucleic acid ((RNA) polymerase gene was introduced into the dnaA mutant, demonstrating that RNA polymerase synthesizes one or more RNA species required for the initation of DNA replication (origin-RNA). Reinitiation at 30 degrees C was not inhibited by streptolydigin in a stretolydigin-sensitive dnaA muntant. Incubation in the presence of nalidixic acid prevented subsequent reinitiation in the dnaC28 mutant but did not inhibit reinitiation in the dnaA5 muntant. These results demonstrate that the dnaA gene product acts before or during the synthesis of an origin-RNA, RNA polymerase synthesizes this origin RNA, and the dnaC gene product is involved in a step after this RNA synthesis event. Furthermore, these results suggest that the dnaC gene product is involved in the first deoxyribounucleotide polymerization event wheareas the dnaA gene product acts prior to this event. A model is presented describing the temporal sequence of events that occur during initiation of a round of DNA replication, based on results in this and the accompanying paper.

Repair deficiency, mutator activity, and thermal prophage inducibility in dna-8132 strains of Bacillus subtilis

A ts mutation, dna-8132 (Hara and Yoshikawa, 1973), in the region of chromosome replication origin of Bacillus subtilis was found to cause pleiotropic effects at a permissive temperature (30 C). Strains carrying this mutation were lethan at 48 C but exhibited higher spontaneous mutation frequency and a lower capacity for repairing radiation damages at 30C. Introduction of the polA59 (Gass et al., 1971) mutation further enhanced the repair deficiency and the mutator activity. These results suggest that the dna-8132 gene product may be directly involved in chromosome replication and repair. SPO2 lysogens carrying this mutation produced mature phages upon a temperature shift from 30 to 48 C. Phage production at nonpermissive temperature suggests that there are few defects in the precursors of deoxyribonucleic acid synthesis in the mutant.

Stimulation of adenosine 5'-triphosphate-dependent in vitro deoxyribonucleic acid replication by factors from the periplasmic space of Escherichia coli

In vitro deoxyribonucleic acid (DNA) synthesis systems based on an earlier system using pencillin have been developed which use osmotic lysis of lysozyme-formed spheroplasts of Escherichia coli cells embedded in an agarose matrix. An adenosine 5'-triphosphate (ATP)-dependent semiconservative mode, or replicative mode, of in vitro DNA synthesis is exhibited which is sensitivie to nalidixic acid. These systems require growth of the agar-embedded cells in a preincubation medium before spheroplast formation and osmotic lysis. Inhibitor studies suggest that one or more required macromolecular species are synthesized during this preincubation growth period. Osmotic shock fluid from E. coli contains macromolecular factors which preferentially stimulate the ATP- dependent semiconservative mode of in vitro DNA synthesis. In some cases, the ATP independent mode of synthesis is inhibited by shock fluid. Evidence is presented that the stimulating factors found in the osmotic shock fluid come from the E. coli periplasmic space. This stimulation is observed using either toluene-treated cells or lysed agar-embedded ethylene glycol-bis-(beta-aminoethyl ether) N,N'-tetraacetate-lysozyme spheroplasts, and is thus independent of the in vitro DNA synthesis system used. Shock fluid obtained from a given E. coli dna mutant does not stimulate in vitro DNA synthesis by that mutant. However, in some cases, shock fluid from one class of dna mutants does stimulate ATP dependent in vitro DNA synthesis by another class of dna mutants, in a thermosensitive reacaction. Gently prepared cell extracts also stimulate ATP-dependent in vitro DNA synthesis, whereas cell extracts prepared by more severe procedures inhibit this in vitro synthesis. Severl stimulating DNA replication factors may be present in the osmotic shock fluid, including products of E. coli dna genes.