![]() ![]() ![]() We therefore prepared a 16-subunit core Mediator complex (cMed) and bound it to a preassembled yeast PIC ( 5, 7) that was extended by a +1 nucleosome as recently reported ( 15). Comparisons with the human PIC-Mediator structure show that the central region in peptide 1 is similar and forms conserved contacts with Mediator, whereas peptides 2 and 3 exhibit distinct structures and Mediator interactions.ĭespite enormous efforts over the years, there is currently no protocol to obtain well-defined, complete recombinant yeast Mediator for structural studies. The third CTD region (peptide 3) binds in the Mediator cradle and associates with the Mediator hook. ![]() CTD peptide 1 binds between the Med6 shoulder and Med31 knob domains, whereas CTD peptide 2 forms additional contacts with Med4. Two of these CTD regions bind between the Mediator head and middle modules and form defined CTD–Mediator interactions. We observe three peptide regions containing eleven of the 26 heptapeptide repeats of the flexible C-terminal repeat domain (CTD) of Pol II. Here, we present an atomic model for the yeast PIC with core Mediator, including the Mediator middle module that was previously poorly resolved and including subunit Med1 that was previously lacking. Whereas atomic models of the human PIC-Mediator structure have been reported, structures for its yeast counterpart remain incomplete. For transcription initiation, RNA polymerase II (Pol II) forms a preinitiation complex (PIC) that associates with the general coactivator Mediator. ![]()
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