Regulation of Deoxyribonucleic Acid Replication and Cell Division in Escherichia coli B/r

Abstract

Synchronous cultures of Escherichia coli strain B/r were used to investigate the relationship between deoxyribonucleic acid (DNA) replication and cell division. We have determined that terminal steps in division can proceed in the absence of DNA synthesis. Inhibition of DNA replication with nalidixic acid prior to the start of a new round of replication does not stop cell division, which indicates that the start of the round is not essential in triggering cell division. Inhibition of DNA replication at any time prior to the termination of a round of replication completely blocks cell division, which suggests that there may be a link between the end of the replication cycle and the commitment of the cell to divide. Studies that use a temperature-sensitive mutant which is unable to synthesize DNA at the nonpermissive temperature are in complete agreement with those that use nalidixic acid to inhibit DNA synthesis. This adds support to the idea that the treatments employed limit their action to DNA synthesis. Investigation of minicell production indicates that the production of minicells is blocked when DNA synthesis is inhibited with nalidixic acid. Although nuclear segregation is not required for cell division, DNA synthesis is still required to trigger division. The evidence presented suggests strongly that (i) DNA synthesis is essential for cell division, (ii) the end of a round of replication triggers cell division, and (iii) there is considerable time lapse (one-half generation) between the completion of a round of DNA replication and physical separation of the cells.

Replication and Transfer of the R Factor in a Synchronized Culture of Escherichia coli

“…auxotroph by using amino acid starvation [12]. The doubling time of the chromosomal DNA was about 120 min [7]; this approximately corresponding with our experimental data. It was shown that in E. coli K12, the initiation point of the chromosome replication was found to be located between the lysine and histidine markers, and the order of replication was clockwise [1,4].…”

Enzymes Synthesizing and Hydrolyzing Murein in Escherichia coli

“…In this study, we have assumed, as have others (see [4]), that minicells are typical cell poles. This assumption is based on the observation that minicells are always produced at the cell poles and that the process of septation at the poles is apparently normal as judged by electron microscopy [4] and is under the same controls as division at the center of the cell [23,24,4]. In addition, murein synthesis at these polar sites appears to be normal since the murein composition (both the glycan chain length [25] and the degree of peptide cross-bridging [ll]) is typical.…”

Thioredoxin and related proteins in procaryotes

“…These constructions grow on a rich medium with added glutathione or cysteine. In addition, the cells showed the long filamentous morphology which is characteristic of impaired DNA synthesis [116]. These results suggest that glutaredoxin is essential for ribonucleotide reduction and the preferred cofactor for ribonucleotide reductase in vivo.…”