Head Size Determination and the Morphogenesis of Satellite Phage P4

Abstract

Satellite phage P4 is a virus which can only make plaques on E. coli strains which carry P2 or a related helper prophage (Six, 1963; Six and Klug, 1973). P4 requires all the head and tail genes of its helper prophage for Open image in new window successful lytic multiplication (Six, 1975). As expected from this genetic data, satellite and helper phages appear similar under the electron microscope (Fig. 1; Inman et al., 1971). However, the satellite phage head is smaller than the head of its helper, and contains a smaller genome (m.w. = 7 × 106 daltons, in contrast to 22 × 106 daltons for the P2 helper genome; Inman and Bertani, 1969; Inman et al., 1971). The P2 and P4 genomes are not homologous, since they show ≦ 1% cross-hybridization (Lindqvist, 1974). The small P4 head is never found in cells infected by the helper phage P2 alone. Thus, satellite phage P4 carries the potential for specific head size determination (Gibbs et al., 1973).