9.B.78 The Minor Capsid Protein, gp7, of Bacillus subtilis Phage SPP1 (gp7) Family
Gp7 is a minor capsid protein of the Bacillus subtilis bacteriophage SPP1. Homologous proteins are found in numerous phages. Deletion of gene 7 from the SPP1 genome yielded a mutant phage (SPP1del7) with reduced burst-size. SPP1del7 infections led to normal assembly of virus particles whose morphology, DNA and protein composition was undistinguishable from wild-type virions. However, only approximately 25% of the viral particles that lack gp7 were infectious (Vinga et al., 2006). SPP1del7 particles caused a reduced depolarization of the B. subtilis membrane in infection assays suggesting a defect in virus genome traffic to the host cell. A higher number of SPP1del7 DNA ejection events led to abortive release of DNA to the culture medium when compared with wild-type infections. DNA ejection in vitro showed that no detectable gp7 is co-ejected with the SPP1 genome and that its presence in the virion correlated with anchoring of released DNA to the phage particle. The release of DNA from wild-type phages was slower than that from SPP1del7 suggesting that gp7 controls DNA exit from the virion. This feature is proposed to play a central role in supporting correct routing of the phage genome from the virion to the cell cytoplasm (Vinga et al., 2006). Antiviral agents, BIT225, benzamine, amantadine and NN-DNJ all interact with a heptameric form of p7 (Dahl et al. 2017).
gp7 facilitates the transport reaction:
Phage DNA (phage particle) → Phage DNA (host cytoplasm)