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

Antimicrobial Research Centre and Department of Biochemistry and Biomedical Sciences, McMaster University, 1200 Main Street West, Hamilton, Ontario, Canada L8N 3Z5

^* To whom correspondence should be addressed. Email: ebrown{at}mcmaster.ca.

	Abstract

The Escherichia coli protein YjeQ is a circularly permuted GTPase that is broadly conserved in bacteria. An emerging body of work suggests that YjeQ is involved in ribosome function, namely co-fractionation and in vitro binding to the ribosome, altered polysome profiles on YjeQ depletion and stimulation of GTPase activity by ribosomes. Strains lacking YjeQ are severely compromised for growth in culture. Here, we have 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 yjeQ strain. Screening for suppressors in an ordered library of 374 clones overexpressing essential genes and genes associated with ribosome function revealed that two GTPases, Era and IF2, ameliorated the growth and polysome defects of the yjeQ strain. In addition, seven bona fide enhancers of slow growth were identified (tgt, ksgA, ssrA, rimM, rluD, trmE/mnmE or trmU/mnmA) among 39 deletions (in genes associated with ribosome function) that we constructed in the yjeQ genetic background. Taken in context, our work is most consistent with a role for YjeQ in late 30S subunit biogenesis.