Replacement of the sequence G-T-phi-C-G(A)- by G-A-U-C-G- in initiator transfer RNA of rabbit-liver cytoplasm.

Eukaryotic cytoplasmic initiator tRNAs lack the sequence G-T-Psi-C-G(A)-, which is in every tRNA of known sequence that is active in protein biosynthesis. In initiator tRNA of yeast cytoplasm, which is the only eukaryotic initiator tRNA of known sequence, this sequence is replaced by G-A-U-C-G-. We now report the sequence of a 30-nucleotide-long, 3'-terminal fragment of cytoplasmic initiator tRNA of rabbit liver obtained by specific cleavage of the tRNA at the site occupied by the modified nucleoside, 7-methyl guanosine. We show (i) that in rabbit-liver initiator tRNA also, the sequence G-T-Psi-C-G(A)- is replaced by G-A-U-C-G- and (ii) that the sequences of loop IV of both the yeast and rabbit-liver cytoplasmic initiator tRNAs are identical, A-U-C-G-m(1)-A-A-A-.