| Abstract: | Rabbit globin alpha and beta chains were labeled with 3H]leucine, and with 35S] -methionine from reticulocyte tRNAMet isoacceptors using a rabbit reticulocyte cell-free synthesis system. 35S]Methionine from the three tRNAMet species isolated by RPC-5 chromatography was incorporated into internal positions of both alpha and beta globin. The initiator tRNA, tRNAIMet, exhibited very low efficiency for incorporating methionine internally, while tRNAIIMet was four times more efficient than tRNAIIIMet. Amino acid analysis of the tryptic peptides of the labeled globins revealed that all three isoacceptors incorporated methionine into the normal methionine peptides. Similar studies with Escherichia coli 35S]Met-tRNAfMet showed a 3-fold increase over the reticulocyte initiator tRNA in its capacity to incorporate methionine into the internal positions of rabbit globin. |
