PMID:15110523

Citation	Isidro, A, Henriques, AO and Tavares, P (2004) The portal protein plays essential roles at different steps of the SPP1 DNA packaging process. Virology 322:253-63
Abstract	A large number of viruses use a specialized portal for entry of DNA to the viral capsid and for its polarized exit at the beginning of infection. These families of viruses assemble an icosahedral procapsid containing a portal protein oligomer in one of its 12 vertices. The viral ATPase (terminase) interacts with the portal vertex to form a powerful molecular motor that translocates DNA to the procapsid interior against a steep concentration gradient. The portal protein is an essential component of this DNA packaging machine. Characterization of single amino acid substitutions in the portal protein gp6 of bacteriophage SPP1 that block DNA packaging identified sequential steps in the packaging mechanism that require its action. Gp6 is essential at early steps of DNA packaging and for DNA translocation to the capsid interior, it affects the efficiency of DNA packaging, it is a central component of the headful sensor that determines the size of the packaged DNA molecule, and is essential for closure of the portal pore by the head completion proteins to prevent exit of the DNA encapsidated. Functional regions of gp6 necessary at each step are identified within its primary structure. The similarity between the architecture of portal oligomers and between the DNA packaging strategies of viruses using portals strongly suggests that the portal protein plays the same roles in a large number of viruses.
Links	PubMed Online version:10.1016/j.virol.2004.02.012
Keywords	Amino Acid Substitution; Bacillus Phages/physiology; Bacillus subtilis/virology; Capsid/metabolism; DNA Packaging; Mutation; Sequence Analysis, DNA; Viral Proteins/chemistry; Viral Proteins/genetics; Viral Proteins/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BPSPP:PORTL		GO:0098006: viral DNA genome packaging, headful	ECO:0000315:		P		Table 2 demonstrates gp6 single amino acid substitutions affecting the packaging of sizX chromosome.	complete CACAO 11418
BPSPP:PORTL		GO:0019073: viral DNA genome packaging	ECO:0000315:		P		Figure 3 demonstrates "Arrowheads show the mature DNA produced upon complementation with the sizX allele (1), mature DNA resulting from background effects under our experimental conditions (see text) (2), DNA packaged in presence of gp6 mutant forms that caused a low efficiency phenotype (3), and DNA packaged in presence of a gp6Siz mutant protein (4)."	complete CACAO 11556

References

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