A minor capsid protein P30 is essential for bacteriophage PRD1 capsid assembly.

Bacteriophage PRD1 is a double-stranded DNA virus infecting Gram-negative hosts. It has a membrane component located in the interior of the isometric capsid. In addition to the major capsid protein P3, the capsid contains a 9 kDa protein P30. Protein P30 is proposed to be located between the adjacent facets of the icosahedral capsid and is required for stable capsid assembly. In its absence, an empty phage-specific membrane vesicle is formed. The major protein component of this vesicle is a phage-encoded assembly factor, protein P10, that is not present in the final structure.

Bacteriophage PRD1 DNA entry uses a viral membrane-associated transglycosylase activity.

Amino acid sequence analyses have indicated that the amino-terminal part of bacteriophage PRD1 structural protein P7 carries a conserved transglycosylase domain. We analysed wild-type PRD1 and different mutant particles in zymograms and found a glycolytic activity that was associated with protein P7. This is the first time a putative bacteriophage or plasmid lytic transglycosylase has been shown to have an enzymatic activity. In the absence of protein P7, the phage DNA replication and host cell lysis were delayed. Gene VII of PRD1 is known to encode proteins P7 and P14. In this investigation, the open reading frame coding for P14 was mapped to the 3' end of gene VII. Proteins P7 and P14 probably form a heteromultimeric complex, which is located at the particle vertices and is involved in the early steps of the PRD1 life cycle

Bacteriophage PRD1 contains a labile receptor-binding structure at each vertex.

Bacteriophage PRD1 is a membrane-containing virus with an unexpected similarity to adenovirus. We mutagenized unassigned PRD1 genes to identify minor capsid proteins that could be structural or functional analogs to adenovirus proteins. We report here the identification of an amber mutant, sus525, in an essential PRD1 gene XXXI. The gene was cloned and the gene product was overexpressed and purified to near homogeneity. Analytical ultracentrifugation and gel filtration showed that P31 is a homopentamer of about 70 kDa. The protein was shown to be accessible on the virion surface and its absence in the sus525 particles led to the deficiency of two other viral coat proteins, protein P5 and the adsorption protein P2. Cryo-electron microscopy and image reconstruction of the sus525 particles indicate that these proteins are located on the capsid vertices, because in these particles the entire vertex structure was missing along with the peripentonal major capsid protein P3 trimers. Sus525 particles package DNA effectively but loose it upon purification. All of the PRD1 vertex structures are labile and potentially capable of mediating DNA delivery; this is in contrast to other dsDNA phages which employ a single vertex for packaging and delivery. We propose that this arises from a symmetry mismatch between protein P2 and the pentameric P31 in analogy to that between the adenovirus penton base and the receptor-binding spike.