Expression of a cloned bovine growth hormone gene in Escherichia coli minicells.

The synthesis of polypeptides in Escherichia coli minicells, directed by a pBR322 plasmid and its derivative-carrying bovine growth hormone cDNA insert, was studied. Two polypeptides coded by the ampicillin-resistance (Apr) gene (32 000 and 28 000 daltons) and a tetracycline-resistance (Tcr) polypeptide (36 000 daltons) were identified by insertion inactivation. Two additional polypeptides of 37 000 and 34 000 daltons of as yet unknown function were detected in all extracts regardless of the presence of the Apr or Tcr genes in the plasmid. The pBR322-BGH recombinant plasmid coded for several novel polypeptides, among them one of 46 000 daltons, presumably a fused product of the BGH and beta-lactamase genes. This protein, however, was not secreted into the periplasmic space of the cells as was the beta-lactamase.