First published online August 13, 2003
Journal of Cell Science 116, e1801 (2003)
Copyright © 2003 The Company of Biologists Limited
Mediator: the middleman in transcription
Stimulation of transcription in vivo requires coactivator proteins. These
include chromatin remodellers, histone acetyltransferases and mediator - a
complex that links transcriptional activators with the general transcription
machinery. In a Commentary on
p. 3667, Brian Lewis
and Danny Reinberg review work that is shedding light on the roles of the
mediator and its different components. Recent studies indicate that the timing
of mediator recruitment varies, depending on the promoter. This might reflect
the existence of different types of preinitiation complex or different
mediator complexes. Indeed, mediator has been shown to comprise distinct
functional modules (Srb4, Gal11/Sin4 and Med9/Med10), and studies in various
organisms indicate that particular components are required for specific
developmental processes. Moreover, transient expression assays reveal a
similar dependence of activators on different mediator proteins. In yeast, for
example, transactivation by the VP16 transcription factor requires three
mediator components (Med2p, Pgd1p and Sin4p), whereas GCN4 uses only one
(Sin4p). Lewis and Reinberg propose a model for mediator function that
accounts for these observations: they suggest it acts as a transcriptional
scaffold whose configuration depends on the activators present at the promoter
and ultimately influences the magnitude of transcription.
Related articles in JCS:
- The mediator coactivator complex: functional and physical roles in transcriptional regulation
- Brian A. Lewis and Danny Reinberg
JCS 2003 116: 3667-3675.
[Abstract]
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