The small nonstructural protein (NS2) of the parvovirus minute virus of mice is required for efficient DNA replication and infectious virus production in a cell-type-specific manner.

Seven mutations which affect only the small nonstructural protein NS2 were introduced into the infectious clone of the autonomous parvovirus, minute virus of mice (MVM). The majority of these mutants were severely defective for replication following transfection of normal host murine A9 fibroblasts; however, all were found to replicate more efficiently and produce infectious virus in certain other cell types, including human NB324K. The isolation of viral stocks from NB324K cells permitted a more detailed analysis of the mutant defect on A9 cells. NS2 mutant NS2-2018 was shown to be approximately 10-fold deficient for viral monomer replicative-form DNA production within a single-burst cycle in infected A9 cells and produced a reduced amount of progeny single strand. Mutant NS2-2018 generated wild-type levels of monomer replicative-form DNA on NB324K cells but made reduced levels of progeny single strand and small plaques on these cells. The accumulation of NS1 is reduced late in NS2-2018 infection of A9 cells, but NS1 accumulates to wild-type levels late in NB324K cell infections. NS1 nuclear localization is not dependent on NS2 in A9 or NB324K cells. These results indicate that NS2 participates in MVM DNA replication and is required for efficient viral growth. The requirement for NS2 during MVM replication is also host cell specific. This requirement is significantly more pronounced in the normal host murine A9 cells than in certain other cell types, including NB324K.