Identification, Expression Pattern, and Subcellular Location of Human RIP Isoforms

XRIP alpha was identified as an adapter protein involved in RAP nuclear import. Several homologs were reported in mammal EST analysis, but the expression pattern and genomic organization of hRIP isoforms were not clarified yet. We isolated nine isoforms of hRIP from a premade human fetal brain library. hRIP alpha is the longest isoform with 219 residues, containing a N-terminal arginine-rich basic region, followed by an acidic region and two C-terminal Zn finger-like structures. hRIP beta deletes one Zn-finger-like structure. Three hRIP alpha isoforms and four hRIP sigma isoforms express truncated proteins due to frame shift. hRIP gamma isoforms lost the C-terminal Zn-finger-like structure. hRIP delta isoforms only contain the N-terminal arginine-rich basic region and the core sequence of the acidic region. The genomic organization of hRIP was identified by bioinformatic analysis. hRIP, containing seven exons, is located at human chromosome 17p13. hRIP was expressed in all 16 detected human tissues with a similar pattern. All EGFP-hRIP fusion proteins were located at the nucleus in the HEK293 cell. The two-polar molecular structure of hRIP might be involved in the basic cell function, and plays a role in the alternative nuclear ingress.