Regulation of cell division in Escherichia coli: SOS induction and cellular location of the sulA protein, a key to lon-associated filamentation and death

Abstract

Mutations in sulA (sfiA) block the filamentation and death of capR (ion) mutants that occur after treatments that either damage DNA or inhibit DNA replication and thereby induce the SOS response. Previous suiA-iacZ gene fusion studies showed that sulA is transcriptionally regulated by the SOS response system (lexAlrecA). SulA protein has been hypothesized to be additionally regulated proteolytically through the capR (lon) protease, i.e., in lon mutants lacking a functional ATP-dependent protease there would be more SulA protein. A hypothesized function for SulA protein is an inhibitor of cell septation. To investigate aspects of this model, we attempted to construct Ion, Ion sulA, and Ion sulB strains containing multicopy plasmids specifying the suiA+ gene. Multicopy suIA+ plasmids could not be established in Ion strains because more SulA protein accumulates than in a Ion' strain. When the sulA gene was mutated by a mini-Mu transposon the plasmid could be established in the Ion strains. In contrast, suiA+ plasmids could be established in lon+, lon sulA, and Ion sulB strains. The suiA+ plasmids caused Ion sulA and Ion sulB cells to exist as filaments without SOS induction and to be sensitive to UV light and nitrofurantoin. Evidence implicated higher basal levels of SulA protein in these Ion plasmid suiA + strains as the cause of filamentation. We confirmed that the SulA protein is an 18-kilodalton polypeptide and demonstrated that it was induced by treatment with nalidixic acid. The SulA protein was rapidly degraded in a lon+ strain, but was comparatively more stable in vivo in a lon sulB mutant. Furthermore, the SulA protein was localized to the membrane by several techniques. enzymatic activities: an ATP hydrolysis-dependent protease activity (9, 10; M. F. Charette, Ph.D. thesis, University of Chicago, 1981), DNA stimulated ATPase activity (7a), and nucleic acid-binding activity (56; Charette, Ph.D. thesis). In addition, a defective CapR protein (capR9 allele) has also been purified. The CapR9 protein has retained the general nucleic acid affinity (9, 56), but has lost the protease activity (8,9). In Ion mutants, second site mutations in sul (suppressor of Ion) prevent the filamentation and UV sensitivity without affecting the mucoid phenotype of the cells (14,17,26,27). These mutants were isolated as UV-, nitro-NF-, or methyl methanesulfonate-resistant derivatives of lon strains. The sul mutations are located at two loci on the E. coli chromosome; sulA is near pyrD (22 min), and sulB is near leu (2 min). sfiA and sfiB (sfi for suppressor of filament induction) are identical to sulA and suiB, respectively, and were isolated as spontaneous thermoresistant revertants of tif-1 (recA441) Ion strains (15,23,24). The tif-l Ion strains filament and die at 41°C. To account for their data, George et al. (15) proposed that a division inhibitor (product of the sulA or sulB gene?) was induced by UV and that it might be more stable in Ion strains.By means of a Mu d(amp-lac) operon fusion that linked the structural gene for 3...

Differences in stress response after UVC or UVA irradiation in Vibrio parahaemolyticus

“…Lon is an ATP-dependent protease and is one of the key proteins involved in the E. coli SOS response (Frank et al, 1996;Gonzalez et al, 1998). Lon degrades the SulA protein which is a specific inhibitor of cell division and acts to delay division until DNA repair has taken place in E. coli (D'Ari and Huisman 1983;Schoemaker et al, 1984;Higashitani et al, 1997). Our finding suggests that recA-lexAdependent cell division arrest is observed in V. parahaemolyticus, similar to that in E. coli.…”

SosA inhibits cell division inStaphylococcus aureusin response to DNA damage

“…In rod-shaped bacteria, inhibiting cell division leads to filamentation as a consequence of lateral peptidoglycan synthesis. This phenotype is also observed in E. coli mutants lacking the Lon protease for which SulA is a substrate, further substantiating the role of SulA in cell-division inhibition and filamentation (14,15).…”

“…In rod-shaped bacteria, inhibition of cell division leads to filamentation as a consequence of lateral peptidoglycan synthesis. Such a phenotype is also observed in E. coli mutants lacking the Lon protease for which SulA is a substrate (15,16). For spherical cells such as Staphylococcus aureus little is known of how SOS induction is coupled to cell division.…”

Active degradation of a regulator controls coordination of downstream genes

“…Lon protease knockouts have been shown to increase the mean concentration MarA in E. coli, but affect many other genes in addition to marA (Martin et al 2008;Griffith, Shah & E Wolf 2004a). In order to avoid off-target pleotropic effects from eliminating Lon protease such as cell filamentation (Schoemaker et al 1984), we designed the sgRNA to increase MarA levels, but to produce no qualitative morphological changes to the cell (Fig. S1).…”