Incorporation of methionine from met-tRNA-Met-F into internal positions of polypeptides by mouse liver polysomes.

Abstract

Two methionine accepting tRNA species corresponding to tRNA F Met and tRNA M Met from mouse ascites tumor cells were tested for their ability to donate methionine into internal positions of growing polypeptide chains on mouse liver polysomes. Both tRNA species can function in the elongation of polypeptide chains as judged by their ability to incorporate methionine into protein in the absence of chain initiation. The insertion of methionine into internal positions of polypeptide chains from Met-tRNA F Met was confirmed by Edman degradation and CNBr cleavage. When both tRNA Met species were present in saturating concentrations in the cell-free system a strong preference for the incorporation of methionine from Met-tRNA M Met became apparent.