Structural basis for the recognition of a nucleoporin FG repeat by the NTF2-like domain of the TAP/p15 mRNA nuclear export factor

TAP-p15 heterodimers have been implicated in the export of mRNAs through nu clear pore complexes (NPCs). We report a structural analysis of the interac tion domains of TAP and p15 in a ternary complex with a Phe-Gly (FG) repeat of an NPC component. The TAP-p15 heterodimer is structurally similar to th e homodimeric transport factor NTF2, but unlike NTF2, it is incompatible wi th either homodimerization or Ran binding. The NTF2-like heterodimer functi ons as a single structural unit in recognizing an FG repeat at a hydrophobi c pocket present only on TAP and not on p15. This FG binding site interacts synergistically with a second site at the C terminus of TAP to mediate mRN A transport through the pore. In general, our findings suggest that FG repe ats bind with a similar conformation to different classes of transport fact ors.