Traffic of snRNA follows a complex mechanism involving adaptor proteins. snRNAs are transcribed by the RNA polymerase (Pol) II (with the exception of U6 snRNA which is produced by PolIII) and then they are capped but not polyadenylated. Cap-binding proteins (CBP) 80 and 20 interact with the cap of snRNAs in the nucleus and recruit an export adaptor known as PHAX [178] . This adaptor is phosphorylated and in this state, it is able to interact with CRM1, another member of karyopherin family. This interaction together with the joining of RanGTP is essential for snRNA trafficking [163] . Hydrolysis of RanGTP and dephosphorylation of PHAX lead to the release of the snRNA in the cytoplasm.