The residue immediately upstream of the RNase P cleavage site is a positive determinant

We have studied the importance of the residue at the position immediately upstream of the RNase P RNA cleavage site using model substrates that mimic the structure at and near the cleavage site of the tRNA His precursor. The various model substrates were studied with respect to cleavage site recognition as well as the kinetics of cleavage using M1 RNA, the catalytic subunit of Escherichia coli RNase P. Our studies showed that the identity of the residue immediately upstream of the cleavage site critically influences both these aspects. Among the ones tested, U is the preferred nucleotide at this position. Hence, these findings rationalize why most bacterial tRNA His genes/transcripts harbor a U immediately upstream of the RNase P cleavage site and extend our understanding of the cleavage site recognition process in general and the unusual cleavage of the tRNA His precursor in particular. Based on our as well as the data of others, we suggest that the nucleotide immediately upstream of the cleavage site is a positive determinant for cleavage by RNase P in general and the expression of tRNA genes is influenced by structural elements localized outside the promoter region i.e. in the leader and spacer regions of tRNA transcripts.