Control of Membrane Morphogenesis in Bacteriophage

Abstract

This chapter highlights the advantage of bacteriophages in understanding the control of membrane morphogenesis. With their genomes of relatively small size, the search for a morphological agent is restricted to roughly a dozen gene products. Candidate proteins are identified for PM2 and Φ 6. The membranes of PM2 and the PR4 group of bacteriophages are morphologically similar. The lipid bilayer is sandwiched between the DNA and an external coat of protein—the capsid. Evidence suggests that the membrane is assembled before the DNA is packaged and before the capsid is formed. This fact requires that the size, shape, and lipid composition of the membrane be determined by the physicochemical properties of the membrane components. The membrane of PM2 appears to be derived directly from the cytoplasmic membrane of the host. A model of membrane morphogenesis is considered in which a differentiation of the host membrane is stimulated by a morphogenic protein. The morphogenesis of Φ 6 is very different from that of PM2. In Φ 6, the genetic-morphological evidence clearly indicates preassembly of the nucleocapsid followed by envelopment. There is no capsid. Thus, control of membrane size and shape is determined by the nucleocapsid.