ROLE OF THE NUCLEAR TRANSPORT FACTOR P10 IN NUCLEAR IMPORT

The nuclear import factor p10 was cloned from Saccharomyces cerevisiae and found to be essential. The protein p10 can bind directly to sever al peptide repeat-containing nucleoporins. It also binds to the guanos ine triphosphatase (GTPase) Ran in its guanosine diphosphate (GDP)-bou nd form and to karyopherin beta. Assembly of the karyopherin heterodim er on immobilized nucleoporin yielded cooperative binding of p10 and R an-GDP. Addition of GTP to this pentameric complex led to dissociation of karyopherin alpha, presumably via in situ formation of Ran-GTP fro m Ran-GDP. Thus, p10 appears to coordinate the Ran-dependent associati on and dissociation reactions underlying nuclear import.