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Abstract:
Mediator is a multiprotein co-activator of RNA polymerase
(Pol) II transcription. Mediator contains a
conserved core that comprises the ‘head’ and
‘middle’ modules. We present here a structure–
function analysis of the essential Med11/22 heterodimer,
a part of the head module. Med11/22 forms a
conserved four-helix bundle domain with C-terminal
extensions, which bind the central head subunit
Med17. A highly conserved patch on the bundle
surface is required for stable transcription preinitiation
complex formation on a Pol II promoter
in vitro and in vivo and may recruit the general transcription
factor TFIIH. The bundle domain fold is
also present in the Mediator middle module subcomplex
Med7/21 and is predicted in the Mediator
heterodimers Med2/3, Med4/9, Med10/14 and
Med28/30. The bundle domain thus represents a
common building block that has been multiplied
and functionally diversified during Mediator evolution
in eukaryotes.
