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(iMet)) is used as the primer for copia minus-strand reverse transcription. This primer tRNA(iMet) fragment is thought to be produced by cleavage within the mature tRNA(iMet) sequence. We call this cleavage hyperprocessing. We have previously reported that catalytic RNA of RNase P from Escherichia coli (M1RNA) cleaves the synthetic tRNA(iMet) 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(iMet) prepared from Drosophila adult flies can be cleaved by M1RNA. Using mutant tRNA(iMet) 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.