The bacteriophage Mu gene B product is incorporated into the inner membrane of Escherichia coli.

By using the Triton X-114 method, it could be shown that an Mr 33 000 protein expressed from the left-end EcoRI-C fragment of phage Mu behaves like a hydrophobic protein. Fusion of a DNA region coding for this protein to the controllable pL promoter of phage lambda results in the production of large amounts of the 33-kDal protein under inducing conditions. This protein can be isolated in association with the inner membrane of Escherichia coli cells. Based on complementation studies it was concluded that the 33-kDal protein is the product of the early gene B.