The presence of the glycine-rich sequence in the fivefold channels of MVMi provides a possible mechanism to explain how the unique N-terminal region of VP1 becomes externalized in infectious parvovirions. Residues that determine tropism may form an attachment recognition site for a secondary host-cell factor that modulates tissue specificity. The ordering of nucleotides in a similar region of the interior surface in the CPV and MVMi capsids suggests the existence of a genomic DNA-recognition site within the parvoviral capsid.

No abstract

Two host range switch mutants of the immunosuppressive strain of parvovirus Minute Virus of Mice (MVMi) were isolated from plaques on A9 fibroblasts. Both carried a single coding mutation at residue D399 in VP2, to alanine and glycine in hr105 and hr107, respectively, and a second, non-coding, guanine-to-adenine change at nucleotide 1970 in hr105 and 1967 in hr107. These mutations were recreated in a wild type MVMi infectious plasmid clone, both alone and as pairs, in either the original or switched combinations. All single mutants failed to replicate productively in fibroblasts, but the two pairs of changes were functionally equivalent. Single D399 mutations allowed the viruses to initiate infection in fibroblasts, but NS2 expression was severely restricted and correlated with poor accumulation and release of progeny virus. Mutations at 1967 or 1970 enhanced NS2 accumulation, and allowed efficient progeny production and release. Conversely, the D399 mutations destroyed the viruses' ability to infect EL4 lymphocytes. In all productive EL4 infections, NS2 was expressed at high ratios even in the absence of upstream mutations, and progeny accumulation was efficient. However, EL4 cells lack a mechanism for early progeny release, potentially explaining why virus amplification in these cells is slow.