Component of the Mediator complex, a coactivator involved in regulated gene transcription of nearly all RNA polymerase II-dependent genes. Mediator functions as a bridge to convey information from gene- specific regulatory proteins to the basal RNA polymerase II transcription machinery. Mediator is recruited to promoters by direct interactions with regulatory proteins and serves as a scaffold for the assembly of a functional preinitiation complex with RNA polymerase II and the general transcription factors. Binds to and activates cyclin- dependent kinases CDK8 and CDK19 that phosphorylate the CTD (C-terminal domain) of the large subunit of RNA polymerase II (RNAp II), which may inhibit the formation of a transcription initiation complex. {ECO:0000269|PubMed:16595664, ECO:0000269|PubMed:25344755, ECO:0000269|PubMed:8700522}. This is the function of CCNC (cyclin C, ENSG00000112237).