Protein p1 is membrane associated in infected Bacillus subtilis cells, and the C-terminal region is required for that association, since p1DeltaC43 neither associates with membranes in vivo nor self-interacts in vitro.

p1 binds the primer terminal protein through a region outside the membrane-association and self-assembly determinants, since the truncated p1DeltaC43 still interacts with the terminal protein in vitro.

p1 levels set the rate of phi29 DNA replication in vivo in a dosage-dependent manner, and the proposed model is that the viral replisome attaches to a membrane-associated p1-based structure.

p1 is amphiphilic despite lacking a transmembrane segment, has a peripheral subcellular location by immunoelectron microscopy, and assembles in infected cells into multimers associated with the bacterial membrane.

The membrane-associated p1 structures pre-assemble independently of the other replisome components and are functional, since plasmid-encoded p1 supports replication of a p1-lacking mutant phage.

p1 enhances the rate of in vivo viral DNA replication, and the proposed role of the membrane-assembled phage structure is to provide a specific site for phi29 DNA replication.

Mutants in six phi29 cistrons fail to synthesise phage DNA under restrictive conditions. The full text identifies them as cistrons 1, 2, 3, 5, 6 and 17, and lists sus1(629) among the mutants that did not synthesise phage DNA, so gene 1 is individually named rather than only covered by the count.

Protein products were assigned to ten of the seventeen phi29 cistrons, and the full text places the gene 1 product among the early proteins of the DNA-synthesis cistrons.

Unit-length phi29 DNA is not synthesised on restrictive infection with sus1(629), showing that p1 is needed for viral DNA replication.

The sus1(629) mutation is an ochre codon in ORF-6, which identifies ORF-6 as gene 1 and so ties the sus1 allele used in the 1976 mutant survey to this locus.

Gene 1 yields two products, a 10 kDa protein and a 6 kDa form named delta-1 that arises from an internal in-phase initiation event in the same open reading frame.

Membrane association of p1 requires its hydrophobic C-terminus, since deleting the C-terminal 43 residues abolishes it.

p1, free terminal protein and a fraction of the viral DNA polymerase are recovered together in membrane fractions of infected cells, supporting a membrane-associated multiprotein initiation complex.

p1 self-associates into long protofilaments that pack into highly ordered two-dimensional sheets resembling eukaryotic tubulin and bacterial FtsZ polymers.

The authors conclude that p1 is a component of a viral-encoded, membrane-associated structure that provides the anchoring site for the viral replication machinery, and that p1 influences the rate of phi29 DNA synthesis in a temperature-dependent manner.

Within the coiled-coil region of p1, residues Leu-46, Met-53 and Leu-60 - but not Leu-39 - are each required for assembly into protofilament sheets, and replacing Leu-46 with Val switches the assembly pathway to 10 nm filaments.

gp1 represses expression of the upstream dna genes for the DNA polymerase and the primer protein without changing the amount, size or integrity of the polycistronic mRNA, indicating a post-transcriptional mechanism.

Histidine-tagged gp1 binds RNA in vitro, and the authors conclude that translation of the dna genes is affected by gp1 binding to their mRNA.

Single substitutions in the predicted coiled-coil or hydrophobic regions block formation of large gp1 complexes, and self-association is proposed to be needed for efficient RNA binding and translational repression.

gp1 suppresses synthesis of the phi29 DNA polymerase and primer protein post-transcriptionally.

A functional p1-YFP fusion localises to midcell independently of other phage proteins, colocalises with host FtsZ, and loses midcell localisation in cells not expressing FtsZ, while depletion of PBP2B has no effect.

In the absence of p1, phage DNA replication is impaired, and phi29 DNA accumulates to higher levels in elongated Bacillus subtilis cells.

The curated FUNCTION statement describes p1 as assembling into highly ordered structures that provide a specific site for viral DNA replication and probably anchor the viral replisome to the host membrane, with experimental evidence tags for four publications.

The subcellular location is the host membrane, as a peripheral membrane protein, and the hydrophobic C-terminus is the determinant of host-membrane association.

The entry records two products of the same open reading frame by alternative initiation, a 10 kDa Long form and a 6 kDa Short form (delta-1) missing residues 1-34.