Morphogenesis of the Filamentous Single-stranded DNA Phages

Abstract

One of the most fascinating aspects of the life cycle of the filamentous phages is their extraordinary morphogenesis. Whereas many other viruses, both enveloped and nonenveloped, are assembled in the cell and released by budding or lysis (Casjens and King 1975), the filamentous phages have evolved a different process for the release of their genetic material. They do not form intracellular phage particles; instead, in some way, they extrude their genomes through the bacterial membrane while assembling the capsid subunits around the genome to form the mature virion (for general reviews of the filamentous phage life cycle see Marvin and Hohn 1969; Denhardt 1975; Ray 1977). Approximately 200 phage particles are produced per cell generation without destruction of the host cell. The mature phage particle is about 6 nm in diameter by 1 μm in length and is composed of the phage single-stranded (SS) DNA encapsulated by approximately 2800 molecules of the phage-specified B, or coat (gene-VIII), protein. Approximately four molecules of the A, or adsorption, protein are at one end of the filamentous particle (Rossomando and Zinder 1968; Marco 1975; Goldsmith and Konigsberg 1977; Woolford et al. 1977). There may also be a few copies of another protein in the phage particle, possibly phage-specified and located at the other end of the particle (Pratt et al. 1969; Beaudoin 1970; Kornberg 1974). The structure of these filamentous phage particles is discussed in this volume by Marvin, by Day and Wiseman, and by Makowski and Caspar.

The membrane-associated process of phage...