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Abstract:
The essential core of the transcription coactivator
Mediator consists of two conserved multiprotein
modules, the head and middle modules. Whereas
the structure of the head module is known, the
structure of the middle module is lacking. Here we
report a 3D model of a 6-subunit Mediator middle
module. The model was obtained by arranging
crystal structures and homology models of parts
of the module based on lysine–lysine cross-links
obtained by mass spectrometric analysis. The
model contains a central tetramer formed by
the heterodimers Med4/Med9 and Med7/Med21.
The Med7/Med21 heterodimer is flanked by
subunits Med10 and Med31. The model is highly
extended, suggests that the middle module is
flexible and contributes to a molecular basis for
detailed structure–function studies of RNA polymerase
II regulation.
