Recognition of tRNA bottom half by bacterial ribonuclease P.

Bacterial ribonuclease P (RNase P) contains a catalytic RNA that cleaves precursor tRNA to form the 5'-end of mature tRNA. Bacterial RNase P mainly recognizes the acceptor stem and T arm modules of tRNA molecules. The region consisting of T arm, acceptor stem and 3' CCA motif in the tRNA is generally termed "top half", and the region consisting of the others, anticodon arm, extra loop and D arm, is called "bottom half". The stems in the top half contribute to recognition, but effects of the bottom half have not been elucidated. To study the effects of the bottom half on the RNase P recognition, we have synthesized several mutant substrates that have the bottom half on different positions along the top half stem. Most of these mutants were cleaved by Escherichia coli RNase P precisely at the expected position, but the cleavage efficiencies were very different especially at low Mg2+ concentration. We also found that RNase P holoenzyme prefered somewhat mutated tRNA precursor to the wild-type tRNA precursor.