title: Overexpression of the LexA-regulated tisAB RNA in E. coli inhibits SOS functions; implications for regulation of the SOS response.
abstract: The DNA damage induced SOS response in Escherichia coli is initiated by cleavage of the LexA repressor through activation of RecA. Here we demonstrate that overexpression of the SOS-inducible tisAB gene inhibits several SOS functions in vivo. Wild-type E. coli overexpressing tisAB showed the same UV sensitivity as a lexA mutant carrying a noncleavable version of the LexA protein unable to induce the SOS response. Immunoblotting confirmed that tisAB overexpression leads to higher levels of LexA repressor and northern experiments demonstrated delayed and reduced induction of recA mRNA. In addition, induction of prophage lambda and UV-induced filamentation was inhibited by tisAB overexpression. The tisAB gene contains antisense sequences to the SOS-inducible dinD gene (16 nt) and the uxaA gene (20 nt), the latter encoding a dehydratase essential for galacturonate catabolism. Cleavage of uxaA mRNA at the antisense sequence was dependent on tisAB RNA expression. We showed that overexpression of tisAB is less able to confer UV sensitivity to the uxaA dinD double mutant as compared to wild-type, indicating that the dinD and uxaA transcripts modulate the anti-SOS response of tisAB. These data shed new light on the complexity of SOS regulation in which the uxaA gene could link sugar metabolism to the SOS response via antisense regulation of the tisAB gene.
authors.affiliation: Centre for Molecular Biology and Neuroscience, Institute of Medical Microbiology, Rikshospitalet University Hospital, NO-0027 Oslo, Norway.
authors.forename: Ragnhild
authors.initials: R
authors.lastname: Weel-Sneve
authors.forename: Magnar
authors.initials: M
authors.lastname: Bjørås
authors.forename: Knut Ivan
authors.initials: KI
authors.lastname: Kristiansen
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D010582:Bacteriophage lambda / Q000528:radiation effects; D001483:Base Sequence; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics* / Q000528:radiation effects; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics / Q000302:isolation & purification; D039002:Prophages / Q000528:radiation effects; D016372:RNA, Antisense / Q000737:chemistry; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D011938:Rec A Recombinases / Q000096:biosynthesis / Q000235:genetics; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics; D013014:SOS Response, Genetics; D012697:Serine Endopeptidases / Q000096:biosynthesis* / Q000235:genetics; D014466:Ultraviolet Rays; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D016372:RNA, Antisense; D012333:RNA, Messenger; D011938:Rec A Recombinases; D012097:Repressor Proteins; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein; C087483:dinD protein, E coli