Evidence that small phenylalanine peptides bound to ribosomes are attached to sRNA

Abstract

Phenylalanine- 14C was transferred from phenylalanyl- 14C-RNA in the presence of polyuridylic acid to small peptides of phenylalanine bound to reticulocyte ribosomes. The RNA fraction, containing the labeled products, was isolated from these ribosomes. Centrifugation of this RNA in a sucrose density gradient showed that the 14C-peptides were attached to sRNA-like molecules. The rate of hydrolysis of these labeled products with hydroxylamine suggested that the 14C-peptides were joined by labile ester bonds to the 3′-termini of sRNA molecules. Isolated diphenylalanyl-RNA was six times more stable to hydroxylaminolysis at neutral pH than phenylalanyl-RNA; oligopeptidyl-RNA was only slightly more stable than diphenylalanyl-RNA. Transfer studies with 3H-phenylalanyl- 14C-RNA, having the 3′-terminal adenosine of the sRNA labeled with 14C, revealed that the ribosome-bound phenylalanyl-RNA contained a molar ratio of one phenylalanine- 3H per adenosine- 14C, and that the diphenylalanyl-RNA contained a molar ratio of two phenylalanine- 3H per adenosine- 14C. These results suggest that the phenylalanyl-RNA is transferred to the ribosome as a unit and the growing polypeptide chain remains bound to an sRNA molecule coming originally from the soluble phase.