1.K.2 The PRD1 Phage DNA Delivery (PRD1-DD) Family
Enterobacteriophage PRD1 is a dsDNA virus composed of an outer icosahedral protein shell with an underlying biological membrane that closely follows the shape of the capsid. The protein-rich membrane vesicle encloses the linear 14,926-bp-long genome with proteins covalently attached to both 5'''' termini.
A complex of four proteins is involved in PRD1 DNA entry in four steps: (1) outer membrane (OM) penetration (involving protein P11; gene XI product), (2) peptidoglycan digestion (involving protein P14 (protein P7/14; gene VII product; a lytic enzyme), (3) cytoplasmic membrane penetration (involving proteins P18 (gene product XVIII or ORFm) and P32 (gene product XXXII or ORFn)). These proteins presumably comprise the DNA translocase. It is proposed that the initial stage of entry is powered by the pressure build-up during DNA packaging. P11 is required only for penetration of the outer membrane, but its mechanism of action is unknown. Similarly, P18 and P32, integral viral membrane proteins, comprise at least part of the DNA translocation machinery for transport across the cytoplasmic membrane, but their mechanisms of action are unknown (Grahn et al., 2002). The P32 protein is 53 aas long with a single putative N-terminal TMS. It is 54% identical and 84% similar to protein o of phage PRD1 (Acc #P27390).
The transport reaction catalyzed by the PRD1 phage DNA delivery system is:
DNA (in the phage capsid) → DNA (in the bacterial cytoplasm)