Cloning and characterization of an atypical type IVP-type ATPase that binds to the RING motif of RUSH transcription factors

RUSH proteins are SWI/SNF-related transcription factors with RING finger si gnatures near their COOH termini. Long suspected of mediating protein-prote in interactions, the RING motif was used to clone a binding partner. The RI NG finger binding protein (RFBP) is a Type IV P-type ATPase, a putative pho spholipid pump, with conserved sequences for two loop segments, an ATP-bind ing site, a phosphorylation domain, and transmembrane passes potentially in volved in substrate binding and translocation, However, RFBP differs from a ll other Type IV P-type ATPases in three ways. It has only three of four hi ghly conserved NH2-terminal transmembrane passes, it is located in the inne r nuclear membrane, and it binds the RING domain. Topographically the orien tation of the adjacent hydrophilic domains and the determinants of transpor t specificity are altered. ks a result, the small, hydrophilic loop extends into the perinuclear space that is contiguous with the lumen of the endopl asmic reticulum, The large, conformationally flexible loop extends into the nucleoplasm to contact euchromatin. Competitive reverse transcriptase-poly merase chain reaction and high performance liquid chromatography analysis r evealed that endometrial RFBP mRNA expression is hormonally regulated,The p hysical association of a hormone-dependent RING finger-binding protein with transcriptionally active chromatin supports the speculation that RFBP play s a role in the subnuclear trafficking of transcription factors with RING m otifs.