Filamentous phage pre-coat is an integral membrane protein: analysis by a new method of membrane preparation.

We show, using a simple, rapid fractionation method, that the precursor to the filamentous phage major coat protein is an integral membrane protein. The method, which consists of treatment of Escherichia coli with 0.1 N NaOH followed by centrifugation, leaves a subset of inner and outer membrane proteins in the NaOH pellet. Most proteins partition into the NaOH pellet (membrane) or supernatant (cytoplasm and periplasm) in a manner consistent with their subcellular location as determined by more conventional techniques. We find no evidence for cytoplasmic filamentous phage pre-coat protein in either wild-type of mutant-infected cells. Our evidence suggests that a protein identified as "soluble procoat" by K. Ito, G. Mandell and W. Wickner may be the amber fragment of a different phage protein.