Nuclear receptor coactivator 5 (NCOA5), also known as coactivator independent of AF-2 function (CIA), is a protein that in humans is encoded by the NCOA5 gene.

This gene encodes a coregulator for the alpha and beta estrogen receptors and the orphan nuclear receptor NR1D2. The protein localizes to the nucleus, and is thought to have both coactivator and corepressor functions. Its interaction with nuclear receptors is independent of the AF2 domain on the receptors, which is known to regulate interaction with other coreceptors. Two alternatively spliced transcript variants for this gene have been described. However, the full length nature of one of the variants has not been determined. [provided by RefSeq, Jul 2008].
Function: Nuclear receptor coregulator that can have both coactivator and corepressor functions. Interacts with nuclear receptors for steroids (ESR1 and ESR2) independently of the steroid binding domain (AF-2) of the ESR receptors, and with the orphan nuclear receptor NR1D2. Involved in the coactivation of nuclear steroid receptors (ER) as well as the corepression of MYC in response to 17-beta-estradiol (E2).