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 kinase Cdk8 that phosphorylates 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. Required for leg and eye development and macrochaete specification or differentiation. Component of the Cdk8 module of the Mediator complex, composed of CycC, Cdk8, kto and skd. Expressed both maternally and zygotically during developmental periods of maximal cell division; most abundant in early embryos and low levels in larvae, pupae and adults. Belongs to the cyclin family. Cyclin C subfamily.