Genetic interaction screens with ordered overexpression and deletion clone sets implicate the Escherichia coli GTPase YjeQ in late ribosome biogenesis

The Escherichia coli protein YjeQ is a circularly permuted GTPase that is broadly conserved in bacteria. An emerging body of evidence, including cofractionation and in vitro binding to the ribosome, altered polysome profiles after YjeQ depletion, and stimulation of GTPase activity by ribosomes, suggests that YjeQ is involved in ribosome function. The growth of strains lacking YjeQ in culture is severely compromised. Here, we probed the cellular function of YjeQ with genetic screens of ordered E. coli genomic libraries for suppressors and enhancers of the slow-growth phenotype of a Delta yjeQ strain. Screening for suppressors using an ordered library of 374 clones overexpressing essential genes and genes associated with ribosome function revealed that two GTPases, Era and initiation factor 2, ameliorated the growth and polysome defects of the Delta yjeQ strain. In addition, seven bona fide enhancers of slow growth were identified (Delta tgt, Delta ksgA, Delta ssrA, Delta rimM, Delta rluD, Delta trmE/mnmE, and Delta trmU/mnmA) among 39 deletions (in genes associated with ribosome function) that we constructed in the Delta yjeQ genetic background. Taken in context, our work is most consistent with the hypothesis that YjeQ has a role in late 30S subunit biogenesis.