Dissociation of tsl-tif -Induced Filamentation and recA Protein Synthesis in Escherichia coli K-12

Abstract

In Escherichia coli , expression of the tif-1 mutation (in the recA gene) induces the “SOS response” at 40°C, including massive synthesis of the recA ( tif ) protein, cell filamentation, appearance of new repair and mutagenic activities, and prophage induction. Expression of the tsl-1 mutation (in the lexA gene) induces massive synthesis of the recA protein and cell filamentation at 42°C, although other SOS functions are not induced. In this paper we show that the septation inhibition induced in tif and tsl strains at 42°C is not due to the presence of a high concentration of recA protein since (i) no recA mutants (≤10 −8 ) were isolated among thermoresistant nonfilamenting revertants of a tif-1 tsl-1 strain, (ii) in a tsl-1 zab-53 strain, only the low basal level of recA protein was synthesized at 42°C, yet cell division was inhibited, and (iii) in a tsl-1 recA99 (amber) strain, no recA protein could be detected at 42°C, yet cell division was inhibited. Among suppressors of tsl-tif -induced lethality are mutations at a locus which we call infB , located in the 66- to 83-min region. The infB1 mutation confers a highly pleiotropic phenotype, which is suggestive of a regulatory defect; it suppressed tsl-tif -induced filamentation but not recA protein synthesis, it did not suppress ultraviolet-induced filamentation (in a lon derivative), and it reduced but did not abolish tif -mediated induction of λ prophage and bacterial mutagenesis. The dissociation of tsl-tif -induced septation inhibition and recA protein synthesis in the tif-1 tsl-1 infB1 strain suggests that the control of SOS filamentation may not be strictly identical to the control of recA protein synthesis.