Component of the Mediator complex, a coactivator involved in the regulated 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. The Mediator complex, having a compact conformation in its free form, is recruited to promoters by direct interactions with regulatory proteins and serves for the assembly of a functional pre-initiation complex with RNA polymerase II and the general transcription factors. Binds to G-box (5'-CACGTG-3')-containing regions of target genes promoters (e.g. IAA29 and IAA19). Involved in defining the duration of cell proliferation. Element of a PIF4/HMR/MED14-dependent thermoresponsive process; required for thermomorphogenetic hypocotyl growth in response to daytime warm temperature elicitation by associating to the promoters of thermoresponsive growth-relevant genes (e.g. mainly involved in biosynthesis and signaling of the phytohormone auxin); this process implies also PIF4 and its transcriptional coactivator PTAC12/HMR/PAP5 to promote the expression of target genes