Model proposed of the evolution of the different RNA export pathways throughout eukaryotic history. (A) Early in the history of eukaryotes a single ancestral exportin similar to XPO1 was in charge of nucleocytoplasmic export of all RNAs in a RanGTP-dependent manner. (B) Prior to the emergence of the LECA, different exportins originated and specialized in nucleocytoplasmic export of the different RNA species. (C) In opisthokonts, a further innovation was the emergence of a RanGTP-independent pathway of mRNA export. This pathway relies on the TAP-p15 heterodimer as the transport receptor instead of an exportin, and includes several other adaptors which are restricted to opisthokonts. Each box represents a human/yeast protein.