Over 25 years ago, Pace and coworkers described an
activity called RNase M5 in Bacillus subtilis
cell extracts responsible for 5S ribosomal RNA maturation
(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 conserved among the low
G + C Gram-positive bacteria. We propose that the gene
be named rnmV. The rnmV gene is nonessential.
B. subtilis strains lacking RNase M5 do not make
mature 5S rRNA, indicating that this process is not necessary
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
trimmed to yield mature 5S RNA, RNase M5 cleaves the B.
subtilis equivalent in a double-stranded region to
yield mature 5S rRNA in one step. For the most part, eubacteria
contain one or the other system for 5S rRNA production,
with an imperfect division along Gram-negative and Gram-positive
lines. A potential correlation between the presence of
RNase E or RNase M5 and the single- or double-stranded
nature of the predicted cleavage sites is explored.