Recombination-deficient mutations and thymineless death in Escherichia coli K12: reciprocal effects of recBC and recF and indifference of recA mutations

Abstract

In an approach to characterizing the nature of the lethal event in thymineless death (TLD), rec mutants of Escherichia coli K12 were examined for their sensitivity to TLD. The recB21 and recC22 mutations sensitized cells of the AB1157 line to TLD but not cells of the HF4733 line. This increased sensitivity was not suppressed substantially by either sbcB15 or xonA1 mutation. In contrast, a recF mutation appeared to make cells more resistant to TLD than rec+ cells. Three different recA alleles were shown not to affect TLD appreciably. These results not only provide further support for the view that the site of the lethal event in TLD is cellular DNA, but also strongly suggest the involvement of the recBC and recF gene products in TLD. The apparent indifference of recA mutation implies that the conventional recombination and repair pathways per se are not involved in TLD and that the hypothetical lethal damage to DNA may be unique in nature.

Cloning of the Vibrio cholerae recA gene and construction of a Vibrio cholerae recA mutant

“…Although strain SM105 does not contain any detectable lysogenic vibriophages, it is possible that the strain contains defective phage genomes which are common in V. cholerae strains (5 coli, bacterial cells can be killed by the induction of lysogenic phages, which is in turn due to the proteolytic activity of activa-ted RecA protein (12). Lysogenic cells containing recA mutations are therefore likely to be more resistant to the effects of thymine starvation, while the survival of nonlysogenic E. coli cells is not affected by recA mutations (21).…”

Disintegration of Nascent Replication Bubbles during Thymine Starvation Triggers RecA- and RecBCD-dependent Replication Origin Destruction

“…15), the same daughter-strand gap repair somehow becomes poisonous during T-starvation. The idea that unfinished daughter-strand gap repair is toxic during T-starvation is supported by the following observations: 1) mutations in recF and recO suppress TLD (10,16,17); 2) inactivation of the UvrD helicase, which inhibits the RecFORpromoted ss-gap repair, accelerates TLD (10, 12); 3) T-starvation sensitizes E. coli cells to subsequent UV irradiation (18,19); and 4) formation of branched DNA, dependent on RecA and RecF, is a hallmark of T-starvation (20).…”

“…However, it is still unclear how this attempted ss-gap repair contributes to the prominent formation of double-strand breaks during T-starvation that yields both the observed chromosomal fragmentation and the strong dependence on RecBCD-catalyzed double-strand break repair during the ϳ1.5-h long resistance phase preceding TLD (10,16,21) (Fig. 1A).…”

Thymineless Death Lives On: New Insights into a Classic Phenomenon

“…Although earlier B. subtilis data could have been interpreted in terms of the fragility of the origin itself, the time course of the genome-wide gene dosage profiles in cells undergoing TLD is also consistent with the lesion being initiated in the ribosomal RNA loci nearest oriC, on either side of it, and propagating toward the origin (68,104). The normalized DNA damage from thyA − strains carrying mutations in the recQ, O, J, and F genes, known to suppress TLD to variable extents (90,91), exhibited an inverse relationship with viabilities of those strains. The authors interpreted that to mean that the lower the relative gene dosage inside the region of the lesion, the greater the corresponding loss in viability would be.…”