Involvement of <i>Escherichia coli</i> unconventional G protein, YchF, in cell growth at the stationary phase

YchF is a universally conserved unconventional G protein. It is known to be involved in the translation of leaderless mRNA. However, leaderless mRNA is rare in Escherichia coli under normal culture conditions, so we analyzed E. coli YchF to clarify its function in vivo. First, bioinformatics analysis was performed, and then the growth and survival of ychF mutants were investigated. The results suggest that the functional domains and important amino acid residues of YchF are conserved. We next found that the ychF mutants exhibited delayed re-growth in late stationary phase in the presence of oxidative stress. Moreover, the growth inhibition by catalase overexpression was suggested to be caused by oxidase activity. We found that the E. coli ychF mutants exhibited reduced growth in early stationary phase that was associated with a decreased level of ribosomal 70S subunit. In the ychF mutants, we also found that overproduction of the ribosomal protein S18 inhibited growth, which was further suppressed by overproduction of S11. YchF of E. coli is involved in the regulation of ribosomal 70S levels possibly through interaction with ribosomal proteins S18 and S11 as well as IF-3, suggesting that YchF is important for growth and survival in the early and late stationary phase of growth.