Synthesis in vitro of ribosomal protein S20 and its precursor

Abstract

Two products synthesized in vitro in a system for coupled transcription and translation programmed by DNA from a transducing bacteriophage [.lambda.] carrying the gene for ribosomal protein S20 were purified and characterized. One of these polypeptides appears to be identical with authentic S20 by several criteria, including its electrophoretic and chromatographic mobilities and its ability to bind to 16S RNA. The 2nd polypeptide is less basic than S20, but exhibits all the structural and functional properties of a precursor to S20, including the presence of an additional methionine residue, apparently as N-formylmethionine. It is converted slowly to S20 in cell-free extracts. The persistence of the precursor form of S20 may also be functionally significant. [Escherichia coli was used in the study].