Specific inhibition of bacterial RNase T2 by helix 41 of 16S ribosomal RNA.

Ribonuclease (RNase) T2 is involved in scavenging exogenous RNAs in the periplasmic space of bacteria. In Escherichia coli, although the 30S ribosomal subunit has long been known as a specific inhibitor of RNase T2 (designated as RNase I in E. coli), both the biochemical mechanisms and physiological roles of this interaction remain to be elucidated. Here we show, by creating hybrid ribosomes and mutational studies, that helix 41 (h41) of the E. coli 16S ribosomal RNA has a crucial role in the specific inhibition of RNase I. Notably, h41-mutant strains exhibit a lower survival rate at stationary phase and severe cell lysis when the post-segregation killing protein SrnB is expressed. These phenotypic defects accompany significant RNA degradation caused by RNase I. Thus, h41 in 16S rRNA provides a physiological benefit for the host cells in coping with the potential cytotoxicity of RNase T2.