The sensitivity of the outer and cytoplasmic membranes of Escherichia coli to detergent was examined by isopycnic sucrose density gradient centrifugation. Sodium lauryl sarcosinate (Sarkosyl) was found to disrupt the cytoplasmic membrane selectively under conditions in which Triton X-100 and dodecyl sodium sulfate solubilized all membrane protein. These results were verified by gel electrophoresis; membrane proteins solubilized by Sarkosyl were identical to those of the cytoplasmic membrane. The presence of Mg2+ during treatment with Sarkosyl was found to afford partial protection of the cytoplasmic membrane from dissolution.

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The synthesis of membrane protein after infection with bacteriophage T4 was examined. Protein constituents of both the cytoplasmic and outer membrane are made during the infective cycle. In addition, newly synthesized membrane protein is found in material which has a buoyant density greater than that of either of the two host membrane fractions. Polyacrylamide gel analyses and solubilization studies using the detergent Sarkosyl indicate that synthesis of most of the membrane proteins made during the first 5 min of infection is directed by bacterial genes. New membrane proteins synthesized at times greater than 6 min after infection appear to be distinct from those of the host, and new proteins of the outer membrane are different from those of the inner. Proteins in the new dense membrane fraction are similar to those of the outer membrane.

Proteins that associate with cellular membrane during the first 5 min after infection with bacteriophage T4 were examined. Several procedures, including electrophoretic separations in three sodium dodecyl sulfate polyacrylamide gel systems and inhibition of host protein synthesis by UV irradiation, were employed to distinguish host-specified proteins from those induced by T4. Residual host protein synthesis was found to account for much of the new protein in preparations of the total membrane and for almost all of the newly synthesized protein in the outer membrane. Preliminary evidence indicates that the synthesis of some host membrane proteins is shut off less rapidly than is host synthesis of soluble protein. One host-directed polypeptide of the outer membrane was unique in that its synthesis or incorporation into the membrane was preferentially inhibited by infection. Also, it was found that the detergent Sarkosyl solubilizes all early T4 membrane proteins; this observation provides the basis for a simple procedure for distinguishing phage proteins from host outer membrane proteins.

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