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Genetic Interaction Screens with Ordered Overexpression and Deletion Clone Sets Implicate the Escherichia coli GTPase YjeQ in Late Ribosome Biogenesis ^,

Tracey L. Campbell and Eric D. Brown^*

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

Received 31 October 2007/ Accepted 18 January 2008

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 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 yjeQ strain. In addition, seven bona fide enhancers of slow growth were identified (tgt, ksgA, ssrA, rimM, rluD, trmE/mnmE, and 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 the hypothesis that YjeQ has a role in late 30S subunit biogenesis.

Published ahead of print on 25 January 2008.

Supplemental material for this article may be found at http://jb.asm.org/.

Present address: Lewis-Sigler Institute, Princeton University, Washington Road, 210 Carl Icahn Laboratory, Princeton, NJ 08544-1014.