[Study of the regulation of colicin E1 and K synthesis]

Synthesis of colicins E1 and K and other plasmids was studied using DNA templates of corresponding plasmids in a cell-free system of coupled transcription and translation. Up to 15 plasmid-specific polypeptides differing by molecular weight were detected electrophoretically in conditions of complete denaturation. Samples of polypeptides related to plasmids ColE1 and ColK were similar in size. A complete or partial substitution of plasmid-free cell extracts by plasmid-containing cell extracts in a cell-free system leads to repression of the synthesis of colicins and some other proteins which is indicated by diminishing or complete disappearance of electrophoretic bands of corresponding polypeptides. The repression is relieved by addition of the recA gene protein into a cell-free system. Based on the obtained results, a conclusion is made that the repressors of colicin genes are not strictly specific and are, probably, coded by plasmids.