The minor capsid protein VP1 of the autonomous parvovirus minute virus of mice is dispensable for encapsidation of progeny single stranded DNA but is required for infectivity

The two capsid proteins of minute virus of mice, VP1 and VP2, are generated from a single large open reading frame by alternate splicing of the capsid gene mRNA. Examination of the replication of a series of mutants that express only VP1, only VP2, or neither capsid protein demonstrates that VP2 is necessary for the accumulation and encapsidation of virus progeny single-stranded DNA. VP1 is dispensable for these functions but is required to produce an infectious virion. Virus that lacks VP1 binds to cells as efficiently as wild-type minute virus of mice but fails to initiate a productive infection. Because neither capsid protein is required for viral-DNA replication, these results suggest that virus lacking VP1 is blocked at a step during virus entry, subsequent to cell binding and prior to the initiation of DNA replication. Minute virus of mice (MVM) is a small, nonenveloped, T = 1 icosahedral virus approximately 22 nm in diameter that packages a single negative-sense strand of DNA (15, 61). The viral capsid proteins VP1 and VP2 are translated from the viral R3 mRNAs generated from a promoter at map unit 38 (2, 31). The ratio of VPl to VP2 found in both infected cells and assembled capsids depends on which splice dono