The nucleotide sequence of the dimeric precursor to glutamine and leucine transfer RNAs coded by bacteriophage T4

Abstract

The nucleotide sequence of a precursor to glutamine and leucine transfer RNAs coded by bacteriophage T4 is presented. The sequence derivation relied on, and was thus facilitated by, knowledge of the previously determined sequences of the mature tRNAs. The molecule is dimeric; the single polynucleotide chain contains the sequences present in two tRNA species. The dimer contains only six precursor-specific residues, all of which are present at the 5′ terminus. The 3′ C-C-A OH terminus of the mature leucine tRNA is present at the 3′ end of the precursor. In contrast, the 3′ terminal C-C-A sequence of mature glutamine tRNA is not found in the precursor and must therefore be added post transcriptionally. The dimeric precursor can undergo endonucleolytic cleavage by purified ribonuclease P to generate the correct 5′ termini of the mature tRNAs. Sequence comparisons with other phage and bacterial tRNA precursors known to be substrates for this enzyme force the conclusion that recognition by RNAase P is other than sequence-specific.