MED6 is an essential for viability component of the head module of the yeast mediator complex. It is involved in bridging between the head and tail modules of mediator. A mutation of MED6 in yeast abolished activation of transcription of 5 inducible promoters in vivo, but this mutation had no effect on uninduced transcription, transcription of constitutively expressed genes, or transcription by RNA polymerases I and III (PMID:9234719). MED6 specifically interacts with Srb4, and this interaction is a requirement for transcriptional regulation of the RNA pol II holoenzyme (PMID:9710620).