Ran GTPase is required for nucleocytoplasmic transport of many types of cargo. Several proteins that recognize Ran in its @entity3007 -bound state (Ran x @entity3007 ) possess a conserved Ran-binding domain (RanBD). Ran-binding protein-1 ( @entity68613 ) has a single RanBD and is required for RanGAP-mediated @entity3007 hydrolysis and release of Ran from nuclear transport receptors (karyopherins). In budding @entity375 ( @entity375 ), @entity68613 is encoded by the essential @entity68614 gene; expression of @entity19 @entity68613 cDNA rescues the lethality of @entity68614 -deficient cells. We generated libraries of @entity19 @entity68613 mutants and examined 11 mutants in vitro and for their ability to complement a temperature-sensitive @entity68614 mutant ( @entity68614 -51(ts)) in vivo. In 9 of the mutants, the alteration was a change in a residue (or 2 residues) that is conserved in all known RanBDs. However, 4 of these 9 mutants displayed biochemical properties indistinguishable from that of wild-type @entity68613 . These mutants bound to Ran x @entity3007 , stimulated RanGAP, inhibited the exchange activity of RCC1, and rescued growth of the @entity68614 -51(ts) @entity375 cells. Two of the 9 mutants altered in residues thought to be essential for interaction with Ran were unable to rescue growth of the @entity68614 (ts) mutant and did not bind detectably to Ran in vitro. However, one of these 2 mutants (and 2 others that were crippled in other @entity68613 functions) retained some ability to co-activate RanGAP. A truncated form of @entity68613 (lacking its nuclear export signal) was able to complement the @entity68614 (ts) mutation. When driven from the @entity68614 promoter, 4 of the 5 mutants most impaired for Ran binding were unable to rescue growth of the @entity68614 (ts) cells; remarkably, these mutants could nevertheless form ternary complexes with importin-5 or importin-beta and Ran- @entity3007 . The same mutants stimulated only inefficiently RanGAP-mediated @entity3007 hydrolysis of the Ran x @entity3007 x importin-5 complex. Thus, the essential biological activity of @entity68613 in budding @entity375 correlates not with Ran x @entity3007 binding per se or with the ability to form ternary complexes with karyopherins, but with the capacity to potentiate RanGAP activity toward @entity3007 -bound Ran in these complexes.

Random mutagenesis and functional analysis of the Ran-binding protein, XXXX .

@entity3007 :: ('MESH:D006160', 'Chemical') :: ['GTP'] @entity68614 :: ('851565(Tax:4932)', 'Gene') :: ['yrb1', 'Yrb1', 'YRB1'] @entity19 :: ('10090', 'Species') :: ['mouse'] @entity68613 :: ('19385(Tax:10090)', 'Gene') :: ['RanBP1'] @entity375 :: ('4932', 'Species') :: ['yeast', 'Saccharomyces cerevisiae']
@entity68613 :: (19385(Tax:10090),Gene) :: ['RanBP1']
