Genomic organization, expression, and localization of murine Ran-binding protein 2 (RanBP2) gene

The Ran-binding protein 2 (RanBP2) is a giant scaffold and mosaic cyclophil in-related nucleoporin implicated in the RanGTPase cycle. There are no orth ologs of the RanBP2 gene in yeast and Drosophila genomes. In humans, this b ona fide gene is partially duplicated in a RanBP2 gene cluster and lies in a hot spot for recombination on Chromosome (Chr) 2q. This genetic heterogen eity renders further significance of this genomic region in human disease d ue to its possible involvement in genetically linked disorders such as juve nile nephronophthisis, congenital hepatic fibrosis, and chorioretinal dyspl asia. Structure-function studies on bovine RanBP2 indicate that this protei n is involved in integrating nucleocytoplasmic transport pathways with prot ein biogenesis such as production of functional opsin. To gain further insi ght into the complex functions of RanBP2 in the development and function of the neuroretina and other tissues, and proceed towards the functional anal ysis of RanBP2 and its molecular partners in vivo, we have determined the c omplete genomic organization of the murine RanBP2 gene. The gene consists o f 29 exons spread over 50 kb and contains a mega-exon of 4663 bp that encom passes the variable Zn-finger-rich domain of RanBP2. This may account, in p art, for a predisposition of recombination of this locus and variability of the number of Zn-fingers across mammalian species. The RanBP2 promoter con tains tissue-specific elements. A CpG island encompasses this region up to the first intron, making RanBP2 gene expression susceptible of epigenetic r egulation. This murine RanBP2 transcript has a tissue-restricted expression profile, and the conceptual protein is 82% identical to human RanBP2. The gene maps to mouse Chr 10, 30 cM proximal of the centromere.