Loss of Methionine Acceptor Activity Resulting from a Base Change in the Anticodon of Escherichia coli Formylmethionine Transfer Ribonucleic Acid

Abstract

Abstract Treatment of Escherichia coli formylmethionine tRNA with sodium bisulfite at 25° results in the conversion of 6 cytidine (C) residues to uridine (U) residues and loss of amino acid acceptor activity. Separation of active and inactive molecules following modification to the extent of 57% loss of activity has shown that C → U base changes in the dihydrouridine loop and at the 5' terminus have no effect on aminoacylation or formylation of tRNAfmet. Conversion of the cytidine residue in the anticodon to a uridine residue causes complete loss of methionine acceptor activity. In addition, deamination of the cytidine residue closest to the 3' terminus inactivates tRNAfmet while modification of the adjacent cytidine residue in the 3'-terminal C-C-A sequence has no effect on methionine or formate acceptance.