2p8q: Difference between revisions

The nuclear import of uridine-rich ribonucleoproteins (U snRNPs) is mediated by the transport adaptor snurportin 1 (SNP1). Similar to importin alpha, SNP1 uses an N-terminal importin beta binding (sIBB) domain to recruit the receptor importin beta and gain access to the nucleus. In this paper, we demonstrate the sIBB-domain has a bipartite nature, which contains two distinct binding determinants for importin beta. The first determinant spans residues 25-65, and includes the previously identified alphaIBB-region of homology. The second binding determinant encompasses residues 1-24 and resembles region 1011-1035 of the nucleoporin 153 (Nup153). The two binding determinants synergize within the sIBB-domain to confer a low nanomolar binding affinity for importin beta, (Kd ~2nM) in an interaction that, in vitro, is displaced by RanGppNHp. We propose that in vivo the synergy of Nup153 and nuclear RanGTP promotes translocation of U snRNPs into the nucleus.

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