Defects in ribosome function delay the initiation of chromosome replication in Escherichia coli.

The Sra protein is a component of the 30S ribosomal subunit while RimJ is a ribosome-associated protein that plays a role in the maturation of the 30S ribosomal subunit. Here we found that Δsra and ΔrimJ cells showed a delayed initiation of DNA replication, prolonged doubling time, decreased cell size, and decreased amounts of total protein and DnaA per cell compared with these observed for wild-type cells. A temperature sensitivity test demonstrated that absence of the Sra or RimJ protein did not change the temperature sensitivity of the dnaA46, dnaB252, or dnaC2 mutants.

Trans-translation ensures timely initiation of DNA replication and DnaA synthesis in Escherichia coli.

The trans-translation pathway, mediated by the transfer messenger RNA (tmRNA; encoded by the ssrA gene) and the SmpB protein (tmRNA-binding protein expressed in Salmonella enterica), which is conserved in bacteria, is required for various cellular processes. A previous study has shown that trans-translation is required to ensure timely (non-delayed) dnaA transcription and consequent initiation of DNA replication in Caulobacter crescentus. In this study, we observed that initiation of chromosome replication was delayed in Escherichia coli lacking the smpB and/or ssrA genes (DssrA, DsmpB, or DsmpBDssrA mutants).

Absence of the BaeR protein leads to the early initiation of DNA replication in Escherichia coli.

Escherichia coli cells have dozens of two-component systems to sense and respond to various stimuli, and thereby cope with changing environments. BaeS/BaeR is one such two-component system, and it deals with a variety of envelope stresses. Interestingly, the ArcA/ArcB and TorS/TorR two-component systems are known to be associated with initiation of DNA replication; however, the effects of BaeS/BaeR on initiation of DNA replication remain unknown.