Nevertheless, PV 2A pro is not only able to block mRNA export, but also rRNA and snRNA transport. Both 18S rRNA and U2 snRNA accumulate in the nucleus of 2A proexpressing cells in a dose-dependent manner. Most probably, cleavage of Nup98, Nup62 and Nup153 is involved in these effects, since rRNA, snRNA, and mRNA are exported using different cargo receptors and auxiliary proteins (see above) but all of them relay in Nup activity to traverse NPC [163] . Importantly, tRNAs (val-tRNA) are exported normally despite PV 2A pro expression, indicating that some RNA nuclear export pathways are not affected by this viral protease. In fact, Nup98, Nup62, and Nup153 are not directly involved in tRNA export [163] , reinforcing the idea that nucleoporin cleavage plays a central role in the impairment of protein and RNA trafficking by PV (Figure 4) .