Change of plasmid-specified RNA metabolism in a temperature-sensitive escherichia coli rnp a mutant strain

Abstract

Escherichia coli RNase P is a processing enzyme which cleaves tRNA precursors at the 5``-end of the tRNA sequence. It is composed of protein component, C5 protein, and RNA component, M1 RNA. M1 RNA synthesized from a ColEl-related plasmid, which harbors the rnpB gene encoding M1 RNA, was accumulated in E. coli strain A49 carrying the thermosensitive mutation in the rnp A gene encoding C5 protein at nonpermissive temperature. This accumulation of M1 RNA accompanied the accumulation of two small RNAs in the A49 cells. They were designated as RNA X and RNA Y in diminishing size. Their nucleotide sequences were determined by the enzymatic method. Analysis of the RNA sequences showed that RNA X and RNA Y are composed of 96 and 67 nucleotides, respectively and related with RNA I, which is the negative controller of ColE1 plasmid replication. Surprisingly RNA X has the same sequences of RNA Y but differs in containing an extra 29 nucleotides at the 5`` end. These results indicate that RNA X and RNA Y are originated from the ColE1-related plasmid, and suggest that a defect in RNase P function by the rnpA49 mutation is responsible for accumulation of these RNAs, implying the possible involvement of RNase P in controlling the replication of ColE1-type plasmids.