An evolutionarily conserved complex, the Mediator, is a key partner of most transcriptional activators in eukaryotes [1]. Gal11 and ARC105 are Mediator subunits linking specific transcriptional activators to the basal transcription apparatus 2., 3..
Gal11 is part of the proposed “Gal11 module”, in which it has been suggested to be a direct target of several activators [4]. However, the existence of mammalian Gal11-like proteins has been debated 5., 6.. Here we show that three families of sequence segments, corresponding to amino-terminal fungal/plant Gal11-like sequences, animal ARC105, and plant CREB binding protein (CBP)-like sequences, are homologous to the KIX-domain of CBP/p300 co-activators (see http://mendel.imp.univie.ac.at/SEQUENCES/GACKIX for details). These segments are members of the new GACKIX-domain superfamily. Sequence analysis suggests that Gal11- and ARC105-like proteins are homologs and have the same function in Mediator complexes.
