In agreement with the data obtained from PV-infected cells, on PV 2A pro expression in HeLa cells, Nup98 is cleaved faster than Nup62 and Nup153, which suggests the presence of optimal cleavage sites in this protein [17] . Proteolysis of Nup98 in PV-infected cells as well as in cell-free systems generates two different cleavage products of around 50-65 KDa and 35 KDa [16] . There are two optimal cleavage sites in Nup98 for PV 2A pro located between aminoacids 373-374 and 551-552, containing Gly at P1 , Thr at P2, and Leu at P4. Hydrolysis at both sites results in N-and Cterminal products with predicted molecular masses of 37 and 53 or 55 and 35 KDa, in good agreement with the size of the peptides detected experimentally in PV-infected cells and 2A-treated HeLa extracts [16, 17] . An explanation for the delayed kinetics of Nup62 and Nup153 with respect to Nup98 is that optimal PV 2A pro cleavage sites were not found in these Nups (unpublished data). Recently, Park and colleagues have reported that PV 2A pro directly cleaves Nup62 at six different positions rendering multiple proteolytic products. These cleavage sites are located between aminoacids 103 and 298, thus releasing the FG-rich region from the protein core [200] . Functionally, loss of the FG-rich region might make Nup62 inactive for interaction with cargo receptors. This hypothetical mechanism of Nup62 functional decoupling could be extrapolated to Nup98 and Nup153 (Figure 4) . However, it remains unknown whether PV 2A pro is able to directly cleave Nup98 and Nup153 or where cleavage might occur.