TAP binds to the constitutive transport element (CTE) through a novel RNA-binding motif that is sufficient to promote CTE-dependent RNA export from the nucleus

The constitutive transport element (CTE) of the simian type D retroviruses overcomes nuclear retention and allows nuclear export of unspliced viral RN As by recruiting TAP, a host factor which is thought to be required for exp ort of cellular mRNAs, In this report, we show that the first 372 amino aci d residues of TAP, comprising a stretch of leucine-rich repeats, are both n ecessary and sufficient for binding to the CTE RNA and promoting its export to the cytoplasm, Moreover, like the full-length protein, this domain migr ates to the cytoplasm upon nuclear co-injection with the CTE RNA. Together, these results indicate that the CTE-binding domain includes the signals fo r nuclear export. We also describe a derivative of TAP that bears a triple amino acid substitution within the CTE-binding domain and substantially red uces the export of mRNAs from the nucleus. This provides further evidence f or a role for TAP in this process. Thus, the CTE-binding domain of TAP defi nes a novel RNA-binding motif which has dual functions, both recognizing th e CTE RNA and interacting with other components of the nuclear transport ma chinery.