Kinetics of the processing of the precursor to 4·5 S RNA, a naturally occurring substrate for RNase P from Escherichia coli

A study was made of the cleavage by M1 RNA and RNase P of a non-tRNA precursor that can serve as a substrate for RNase P from Escherichia coli, namely, the precursor to 4·5 S RNA (p4·5S). The overall efficiency of cleavage of p4·5S by RNase P is similar to that of wild-type tRNA precursors. However, unlike the reaction with wild-type tRNA precursors, the reaction catalyzed by the holoenzyme with p4·5S as substrate has a much lower K_m value than that catalyzed by M1 RNA with the same substrate, indicating that the protein subunit plays a crucial role in the recognition of p4·5S. A model hairpin substrate, based on the sequence of p4·5S, is cleaved with greater efficiency that the parent molecule. The 3′-terminal CCC sequence of p4·5 S may be as important for cleavage of this substrate as the 3′-terminal CCA sequence is for cleavage of tRNA precursors.