Hyperprocessing of tRNA by the catalytic RNA of RNase P: Cleavage of a natural tRNA within the mature tRNA sequence and evidence for an altered conformation of the substrate tRNA

In the transposon copia-related retrovirus-like particles of Drosophila, a 39-nucleotide-long fragment from the 5′-region of Drosophila initiator methionine tRNA (tRNA_i ^Met) is used as the primer for copia minusstrand reverse transcription. This primer tRNA_i ^Met fragment is thought to be produced by cleavage within the mature tRNA_i ^Met sequence. We call this cleavage hyperprocessing. We have previously reported that catalytic RNA of RNase P from Escherichia coli (MlRNA) cleaves the synthetic tRNA_i ^Met precursor in vitro at several sites within the mature tRNA sequence. Based on this result, we proposed a model for formation of the primer tRNA fragment involving RNase P. Here we show that natural tRNA_i ^Met prepared from DrosophUa adult flies can be cleaved by MIRNA. Using mutant tRNA_i ^Met substrates, we also show that these cleavages are dependent on the occurrence of an altered conformation of the tRNA substrate. This is evidence that a tRNA can exist in aqueous solution at least in part in an altered conformation.