Stringent response processes suppress DNA damage sensitivity caused by deficiency in full‐length translation initiation factor 2 or PriA helicase

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 (ppGpp⁰) greatly aggravated sensitivity, high levels promoted resistance. Moreover, M+ mutations, which suppress amino acid auxotrophy of ppGpp⁰ 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 ppGpp⁰ 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.