In vitro and in vivo products of E. coli lactose permease gene are identical.

The lacY gene product synthesised in vitro is identical to lactose permease isolated from cytoplasmic membranes as determined by apparent molecular weight and N-terminal amino acid sequence. The amino acid composition of the in vivo product agrees well with that predicted from the DNA sequence. The data assign the translational start on the DNA sequence and demonstrate that this protein is processed only by deformylation but not by proteolytic cleavage at the N-terminus.