Affiliation:
1. Dipartimento di Biologia Strutturale e Funzionale, Università degli Studi dell'Insubria, 21052 Busto Arsizio (Va), Italy
Abstract
ABSTRACT
DNA methylation and chromatin modification operate along a common pathway to repress transcription; accordingly, several experiments demonstrate that the effects of DNA methylation can spread in
cis
and do not require promoter modification. In order to investigate the molecular details of the inhibitory effect of methylation, we microinjected into
Xenopus
oocytes a series of constructs containing a human CpG-rich sequence which has been differentially methylated and cloned at different positions relative to a specific promoter. The parameters influencing the diffusion of gene silencing and the importance of histone deacetylation in the spreading effect were analyzed. We demonstrate that a few methylated cytosines can inhibit a flanking promoter but a threshold of modified sites is required to organize a stable, diffusible chromatin structure. Histone deacetylation is the main cause of gene repression only when methylation does not reach levels sufficient to establish this particular structure. Moreover, contrary to the common thought, promoter modification does not lead to the greater repressive effect; the existence of a competition between transactivators and methyl-binding proteins for the establishment of an open conformation justifies the results obtained.
Publisher
American Society for Microbiology
Subject
Cell Biology,Molecular Biology
Cited by
269 articles.
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