RESUMO
Recently, we revealed that the cloverleaf structure of some eukaryotic tRNAs is not always stable in vitro, and the denatured structures of these tRNAs are sometimes detected in bacterial RNase P reactions. We have designated the unusual internal cleavage reaction of these tRNAs as hyperprocessing. We have developed this hyperprocessing strategy as a useful tool for examining the stability of the tRNA cloverleaf structure. There are some common features in such unstable, hyperprocessible tRNAs, and the criteria for the hyperprocessing reaction of tRNA are extracted. Metazoan initiator methionine tRNAs and lysine tRNAs commonly fit the criteria, and are predicted to be hyperprocessible. The RNase P reactions of two metazoan lysine tRNAs from Homo sapiens and Caenorhabditis elegans, which fit the criteria, resulted in resistance to the internal cleavage reaction, while one bacterial lysine tRNA from Acholeplasma laidlawii, which also fits the criteria, was internally cleaved by the RNase P. The results showed that the metazoan lysine tRNAs examined are very stable without base modifications even under in vitro conditions. We also examined the 3'-half short construct of the human lysine tRNA, and the results showed that this RNA was internally cleaved by the enzyme. The results indicated that the human lysine tRNA has the ability to be hyperprocessed but is structurally stabilized in spite of lacking base modifications. A comparative study suggested, moreover, that the acceptor-stem bases should take part in the stabilization of metazoan lysine tRNAs. Our data strongly suggest that the cloverleaf shape of other metazoan lysine tRNAs should also be stabilized by means of similar strategies to in the case of human tRNA(Lys3).
