Molecular characterization of a newly recognized mouse parvovirus

Mouse parvovirus (MPV), formerly known as orphan parvovirus, is a newly recognized rodent parvovirus distinct from both serotypes of minute virus of mice (MVM). Restriction analysis of the MPV genome indicated that many restriction sites in the capsid region were different from those of MVM, but most sites in the nonstructural (NS) region of the genome were conserved. MPV resembled MVM in genome size, replication intermediates, and NS proteins. Replication intermediates in infected cells were the same for MPV and MVM, including packaging of the 5-kb minus (V) strand. Furthermore, the MPV NS proteins were the same size as and present at the same ratio as the MVM(i) proteins in infected cells. Cloning and sequencing of the MPV genome revealed a genome organization closely resembling that of MVM, with conservation of open reading frames, promoter sequences, and splice sites. The left terminal hairpin was identical to that of MVM(i), but the right terminus was not conserved. Also, the MPV genome was unique in that it contained 1.8 copies of the terminal repeat sequence rather than the 1 or 2 copies found in other parvoviruses. The predicted amino acid sequence of the NS proteins of MPV and MVM(i) were nearly identical. In contrast, the predicted amino acid sequence of the capsid proteins of MPV was different from sequences of other parvoviruses. These results confirm that MPV is a distinct murine parvovirus and account for the antigenic differences between MPV and MVM.