title: Stringent response processes suppress DNA damage sensitivity caused by deficiency in full-length translation initiation factor 2 or PriA helicase.
abstract: When Escherichia coli grows in the presence of DNA-damaging agents such as methyl methanesulphonate (MMS), absence of the full-length form of Translation Initiation Factor 2 (IF2-1) or deficiency in helicase activity of replication restart protein PriA leads to a considerable loss of viability. MMS sensitivity of these mutants was contingent on the stringent response alarmone (p)ppGpp being at low levels. While zero levels (ppGpp°) greatly aggravated sensitivity, high levels promoted resistance. Moreover, M+ mutations, which suppress amino acid auxotrophy of ppGpp° strains and which have been found to map to RNA polymerase subunits, largely restored resistance to IF2-1- and PriA helicase-deficient mutants. The truncated forms IF2-2/3 played a key part in inducing especially severe negative effects in ppGpp° cells when restart function priB was knocked out, causing loss of viability and severe cell filamentation, indicative of SOS induction. Even a strain with the wild-type infB allele exhibited significant filamentation and MMS sensitivity in this background whereas mutations that prevent expression of IF2-2/3 essentially eliminated filamentation and largely restored MMS resistance. The results suggest different influences of IF2-1 and IF2-2/3 on the replication restart system depending on (p)ppGpp levels, each having the capacity to maximize survival under differing growth conditions.
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University Medical Center, Box 571455, 3900 Reservoir Rd. NW, Washington, DC, 20057-1455, USA.
authors.forename: K Elizabeth
authors.initials: KE
authors.lastname: Madison
authors.forename: Erica N
authors.initials: EN
authors.lastname: Jones-Foster
authors.forename: Andrea
authors.initials: A
authors.lastname: Vogt
authors.forename: Sandra
authors.initials: S
authors.lastname: Kirtland Turner
authors.forename: Stella H
authors.initials: SH
authors.lastname: North
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakai
mesh_terms: D010583:Bacteriophage mu / Q000235:genetics / Q000502:physiology; D004249:DNA Damage / Q000187:drug effects; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects; D048168:Escherichia coli K12 / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006159:Guanosine Tetraphosphate / Q000494:pharmacology*; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D039881:Prokaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D039881:Prokaryotic Initiation Factor-2; D020033:Protein Isoforms; D006159:Guanosine Tetraphosphate; D008741:Methyl Methanesulfonate; C506743:priA protein, E coli; D004265:DNA Helicases