Transcription and processing of Bacillus subtilis small cytoplasmic RNA

The 271 nucleotides long scRNA (small cytoplasmic RNA) from Bacillus subtilis is structurally related to the Escherichia coli 4.5 S RNA (114 nucleotides), an essential molecule supposed to be involved in protein biosynthesis, but it possesses an additional moiety completely missing in the E. coli 4.5 S RNA. Both RNAs share a conserved hairpin with the eukaryotic 7SL RNAs, which mediate protein translocation as part of the signal recognition particle (SRP). We have cloned and sequenced the entire scRNA gene region from B. subtilis and have studied transcription and processing of the scRNA in B. subtilis by nuclease S1 mapping. This analysis revealed the scRNA gene to constitute a monofunctional transcription unit, expressed from a single promoter to a rho-independent terminator, yielding a precursor which extends the mature scRNA by approximately 40 nucleotides at both ends. Processing of the scRNA apparently involves only two endonucleolytic cuts and occurs first at the 5' end.