Recepin (CIR)

CBF1 (RBPSUH) is a member of the CSL family of DNA-binding factors, which mediate transcriptional activation or repression. Sequence analysis predicted that the 450-amino acid protein contains a highly charged, serine-rich C terminus. Northern blot analysis revealed widespread expression of CIR, with strongest expression detected in heart, skeletal muscle, and pancreas. Immunofluorescence analysis showed that CIR is a nuclear protein like CBF1, although CIR does not bind to the nucleolus. Functional analysis determined that the N-terminal 121 amino acids of CIR interact with amino acids 233 to 249 of CBF1 and repress transcriptional activity. Yeast 2-hybrid and immunofluorescence analyses indicated that CIR also interacts with HDAC2 and SAP30, important mediators of transcriptional repression.