SIP Antibody / SIAH Interacting Protein / CACYBP

CACYBP (Calcyclin-binding protein), also called SIP (SIAH Interacting Protein), is a protein that in humans is encoded by the CACYBP gene. The full-length SIP cDNA encodes a predicted 228-amino acid protein. Sequence analysis of the shortest cDNA derived by 2-hybrid screening revealed an 8-amino acid difference in the deduced open reading frame followed by a stop codon, resulting in a predicted 80-amino acid protein, SIP-short (SIPS) . The CACYBP gene is mapped on 1q25.1. It may be involved in calcium-dependent ubiquitination and subsequent proteosomal degradation of target proteins. It probably serves as a molecular bridge in ubiquitin E3 complexes and participates in the ubiquitin-mediated degradation of beta-catenin. Two alternatively spliced transcript variants encoding different isoforms have been found for this gene. The C-terminal region of SIP that is homologous to SGT1 was able to complement defects in yeast strains containing SGT1 mutant alleles, demonstrating conservation of SGT1 and SIP protein function.