Kinetics of Hyperprocessing Reaction of Human Tyrosine tRNA by Ribonuclease P Ribozyme fromEscherichia coli

Human tyrosine tRNA and fly alanine, histidine, and initiator methionine tRNAs are generally cleavable internally by bacterial ribonuclease P ribozyme. The unusual internal cleavage reaction of tRNA, called hyperprocessing, occurs when the cloverleaf structure of the tRNA molecule is denatured to form a double-hair-pin-like structure. The hyperprocessing reaction of these tRNAs requires magnesium ions. We analyzed details of this reaction using human tyrosine tRNA and Escherichia coli RNase P ribozyme. The usual processing reaction occurred efficiently with magnesium at 5 mM, but for the hyperprpocessing reaction, higher concentrations were needed. With such high concentrations, hyperprocessing cleaved both mature tRNA and tRNA precursor as substrates. When mature tRNA was the substrate, the apparent K(M) was almost the same as in the usual reaction, but k(cat) was smaller. These results indicated that the occurrence of hyperprocessing depends on the magnesium ion concentration, and suggested that magnesium ions contribute to the recognition of the shape of the substrate by bacterial RNase P enzymes.