SUMO1 and infection: To investigate the effect of GCRV infection on the SUMOylation pathway, transcriptional steady state levels of SUMO1, SUMO2 and Ubc9 were determined by real time RT-PCR (Figure 3A, and 3C) during the infection course of GCRV, which was monitored by probing the expression of outer capsid protein VP7 in infected CIK cells (Figure 3D).