A phosphorylated basic vaccinia virion polypeptide of molecular weight 11,000 is exposed on the surface of mature particles and interacts with actin-containing cytoskeletal elements.

A phosphorylated vaccinia virus structural polypeptide of an apparent molecular weight of 11,000 (p11K) was isolated by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and used for antibody induction. After purification by antigen affinity chromatography, the immunoglobulins detected only one target of a rather basic nature in two-dimensional immune blotting procedures of total virion proteins. By use of a combination of biological, biochemical, and microscopic techniques, p11K could be located on the surface of those vaccinia virus particles, with "classical" morphology and a buoyant density of 1.27 g/cm3. Upon immunoprecipitation from radioactively labeled infected cells, p11K appeared to be complexed to two additional virus structural proteins, which could be tentatively identified by their molecular weights as precursors for the two major core constituents. When virus assembly was inhibited by rifampin treatment of infected cells, a great part of p11K, either free or in complexed form, was found associated with actin-containing cytoskeletal elements. The ability of p11K to interact with a not-yet-identified, microfilament-associated cellular protein may be related to previous findings showing that assembled vaccinia particles in situ are found in connection with microfilaments. A possible role for the structures precipitated by p11K-specific antibodies in early stages of particle assembly is discussed.