Initiation of protein synthesis in rabbit reticulocytes

DEAF-Sephadex column chromatography of crude rabbit liver transfer RNA (tRNA) gives rise to three peaks of methionine acceptor activity (met-tRNA MI, met-tRNA MIL , and met-tRNA F).Only one of these species (met-tRNA F) could be charged by E. coli synt hetase and formylated by E coli formylase (1,2). In a cell-free protein synthesizing system obtained from rabbit reticulocytes, [ 14C] met-tRNA F transfers radioactivity to the N-terminal position of the polypeptide chain in response to native messenger RNA. In a similar experiment, [ 14C] met-tRNA MII transfers radioactivity mainly into the internal positions of the synthesized polypeptide chains.