Control of membrane morphogenesis in bacteriophage PM2

The regulation of membrane formation in bacteriophage PM2 serves as a simple model for changes in membrane structure in eukaryotic cells. Prior to Pseudomonas host lysis, wild-type virions mature to an icosahedral morphology at the inner face of the cytoplasmic membrane. The preliminary characterization of two temperature-sensitive mutants of PM2 is described. In cells infected at the restrictive temperature with ts 1, an abundance of "empty" virus-size membrane vesicles are seen. Synthesis of DNA is also reduced in ts 1 infected cells. The preponderance of vesicles is not seen in cells infected with wild-type virus or with ts 1 at the permissive temperature. The "empty" appearance of the viral membranes suggests that viral DNA is not encapsulated. The major viral capsid protein (MW 26,000) is located just outside the viral membrane and normally sidiments with host and virus membranes. This protein made by mutant ts 5 does not pellet with these membranes; instead, large amounts of capsid protein can be precipitated from the supernatant with TCA. Compared to cells infected with wild type virus, cells infected with ts 5 at the restrictive temperature produced inside the cell an abundance of virus-size membrane vesicles. Taken together, these results with viral mutants suggest that formation of a viral membrane of the proper size does not require a DNA core around which to form, or an outer scaffolding of coat protein against which to form a spherical bilayer.