Modification of PCV-2 virulence by substitution of the genogroup motif of the capsid protein

Allemandou, Aude; Grasland, Béatrice; Hernandez-Nignol, Anne-Cécile; Kéranflec'h, André; Cariolet, Roland; Jestin, André

The quantitative PCR results in organs revealed that the replication is not impaired either for the two parental clones or for the two mutants. The genomic loads were lower in the organs of the pigs transfected with the mutant clones than those of the pigs transfected with the parental clones and in the organs of the PCV-2a transfected pigs compared to those transfected with PCV-2b. This demonstrated that the replication efficiency could be different between parental strains and between both parental clones and mutants. One hypothesis to explain this is a differential regulation of the replication step. It was previously showed that the regulation of replication was controlled by the Rep and its own promoter for porcine circovirus [7] . In our study, the Rep and Rep' proteins of the two parental clones had only one amino acid difference. This amino acid was outside of the three motives implicated in the Rep functions [34, 35] and hence might not explain a difference in replication. Nevertheless, in some Geminiviruses, the absence or inactivation of the Cap protein led to reduced accumulation of single-stranded DNA associated with an increase in the level of doublestranded DNA replicative forms [36, 37] . It has been also reported that the Cap protein of the mung bean yellow mosaic India virus, a geminivirus, might have a role in controlling the viral replication and thus the copy number of viral DNA. Indeed, the interaction of its Cap and Rep proteins inhibited the nicking and closing function of the Rep and not the Rep ATPase activity [38] .