Effects of C5 protein on Escherichia coli RNase P catalysis with a precursor tRNA(Phe) bearing a single mismatch in the acceptor stem

Escherichia coli RNase P, an RNA-processing enzyme that cleaves precursor t RNAs to generate the mature 5'-end, is composed of a catalytic component (M 1 RNA) and a protein cofactor (C5 protein). In this study, effects of C5 pr otein on the RNase P catalysis with a precursor E. coli tRNA(Phe) having a single mismatch in the acceptor stem were examined. This mutant precursor u nexpectedly generated upstream cleavage products at the -8 position as well as normal cleavage products at the +1 position. The cleavage at the -8 pos ition was essentially effective only in the presence of C5 protein. Possibl e secondary structures for cleavage at the -8 position deviate significantl y from the structures of the known RNase P substrates, implying that C5 pro tein can allow the enzyme to broaden the substrate specificity more than pr eviously appreciated, (C) 2000 Academic Press.