SUMO2 and infection: However, PCV2 infection significantly promoted the interaction of pNPM1 with SUMO2 and SUMO3, but not with SUMO1 in the cells compared with mock infection (Figs 4D, 4E, 4F and S3), suggesting that PCV2 infection promotes SUMO2/3 conjugation with pNPM1 in the nucleoli of infected cells, but has no obvious effect on SUMO1 and pNPM1 binding.