Conférence du Dr. George Reid
(European Molecular Biology Laboratory, Heidelberg - Allemagne), le
vendredi
4 septembre à 11 h 30, IMM (salle de
conférences Jacques Senez), Campus Joseph Aiguier, Bt IM,
CNRS, Marseille : «Marking time: The dynamic role of
chromatin and covalent modification in transcription».
Résumé :
The expression of genes subject to strict regulation can be a
highly dynamic, cyclical process that sequentially achieves and
then limits transcription. Kinetic investigations of the estrogen
responsive pS2 (TFF1) promoter, to determine the occupancy of
factors or the occurrence of covalent marks on chromatin, have
provided the most comprehensive picture of the complexity of
transcriptional cycling to date.
Cycles are initiated by the assembly of intermediate transcription
factors that in turn provoke conscription of the basal
transcription machinery. These events then achieve activation of
the polymerase II complex, which is subsequently followed by
limitation of productivity through the action of repressive
complexes. This latter phase resets the target promoter, through
acting on chromatin structure, such that a subsequent cycle can be
initiated. In consequence, transcription is dependent upon
cis-acting elements (DNA and nucleosomes) that either interact with
or are modified by trans-acting factors. Induced local structural
changes to chromatin encompassing regulatory elements of gene
promoters include alteration of the positional phasing of
nucleosomes, substitution by variant histones, post-translational
modification of nucleosomes, changes in the methylation of CpG
dinucleotides and breaks in the sugar-phosphate backbone of
DNA.
A primary function of covalent modification of chromatin may be to
drive a sequential progression of reversible interactions that
achieve and regulate gene expression.