Identification of the gene encoding the 5S ribosomal RNA maturase in Bacillus subtilis: Mature 5S rRNA is dispensable for ribosome function

Over 25 years ago, Pace and coworkers described an activity called RNase M5 in Bacillus subtilis cell extracts responsible for 5S ribosomal RNA matura tion (Sogin & Pace, Nature, 1974, 252:598-600). Here we show that RNase M5 is encoded by a gene of previously unknown function that is highly conserve d among the low G + C Gram-positive bacteria. We propose that the gene be n amed rnmV. The rnmV gene is nonessential. a. subtilis strains lacking RNase M5 do not make mature 5S rRNA, indicating that this process is not necessa ry for ribosome function. 5S rRNA precursors can, however, be found in both free and translating ribosomes. In contrast to RNase E, which cleaves the Escherichia coli 5S precursor in a single-stranded region, which is then tr immed to yield mature 5S RNA, RNase M5 cleaves the B. subtilis equivalent i n a double-stranded region to yield mature 5S rRNA in one step. For the mos t part, eubacteria contain one or the other system for 5S rRNA production, with an imperfect division along Gram-negative and Gram-positive lines. A p otential correlation between the presence of RNase E or RNase M5 and the si ngle- or double-stranded nature of the predicted cleavage sites is explored .