YbeX of Escherichia coli, a member of the CorC protein family, is encoded in the same operon with ribosome-associated proteins YbeY and YbeZ. Here, we report the involvement of YbeX in ribosomal metabolism. The ΔybeX cells accumulate distinct 16S rRNA degradation intermediates in the 30S particles and the 70S ribosomes. E. coli lacking ybeX has a lengthened lag phase upon outgrowth from the stationary phase. This growth phenotype is heterogeneous at the individual cell level and especially prominent under low extracellular magnesium levels. The ΔybeX strain is sensitive to elevated growth temperatures and to several ribosome-targeting antibiotics that have in common the ability to induce the cold shock response in E. coli. Although generally milder, the phenotypes of the ΔybeX mutant overlap with those caused by ybeY deletion. A genetic screen revealed partial compensation of the ΔybeX growth phenotype by the overexpression of YbeY. These findings indicate an interconnectedness amongst the ybeZYX operon genes, highlighting their roles in ribosomal assembly and/or degradation.

YbeX of Escherichia coli, a member of the CorC protein family, is a putative Co 2+/ Mg 2+ efflux factor. Here, we describe several ΔybeX phenotypes and report an involvement of YbeX in ribosomal metabolism. E. coli lacking ybeX has a longer lag phase on outgrowth from the stationary phase. This phenotype is heterogeneous at the individual cell level and can be rescued by supplementing the growth media with magnesium. ∆ybeX strain is sensitive to elevated growth temperatures and to several ribosome-targeting antibiotics, which have a common ability to induce the cold shock response in E. coli. ∆ybeX cells accumulate distinct 16S rRNA degradation intermediates present in both 30S particles and 70S ribosomes. We propose that a function of YbeX is maintaining the magnesium homeostasis in the cell, which is needed for proper ribosomal assembly.