Etudes sur le mécanisme de remodelage des nucléosomes par ...

tel-00413908, version 1 - 7 Sep 2009
I.4.3.1.1.1 SWI/SNF
The yeast SWI/SNF complex, considered as the founder for ATP-dependent chromatin
remodeling enzymes, is required by many transcriptional activators to enhance transcription
in yeast (Peterson and Tamkun, 1995; Winston and Carlson 1992). The yeast SWI/SNF
complex consists of 11 subunits viz. SWI1, SWI2/SNF2, SWI3, SNF5, SNF6, SNF11,
SWP82, SWP73, SWP29, ARP7 and ARP9 (Cairns et al., 1994; Cairns et al., 1996a; Côté et
al., 1994; Peterson et al., 1994; Treich et al., 1995). Mutation in ATP binding domain of
Arp7p or Arp9p has shown no phenotypic defect but their deletion mutants are unviable or
show reduced growth (Cairns et al., 1998). Thus, the actin-related proteins Arp7 and Arp9 are
suggested to share structural but not functional similarities with actin and their role has been
implicated in interaction with nuclear matrix.
Several of the yeast SWI/SNF components (Swi2p, Swi3p, Snf5p, Swp73p and the Arp
subunits) have homologous counterparts that are constituents of other SWI/SNF-like
chromatin remodeling complexes. This indicates a functional conservation among these
complexes. However some subunits either show homology in a subset of complexes or are
unique to their complex. For instance, yeast Swi1p shows homology to the OSA and Baf250p
components of Drosophila Brahma and hSWI/SNF (complex A) respectively, whereas Snf6p,
Swp82p, Swp29p and Snf11p appear to be unique to the yeast SWI/SNF complex (Figure
I.15).
Although little is known about the functional role of individual subunits of the SWI/SNF-like
complexes, the size and complexity of these complexes suggest that they perform multiple
functions. SWI/SNF complex displays various ATP-dependent biochemical activities. Despite
the strong homology with the helicases, no strand separation activity is found during the
remodeling (Côté et al., 1994; Quinn et al., 1996; Côté et al., 1998). In an ATP-independent
manner SWI/SNF like complexes have the ability to bind naked and nucleosomal DNA with
high affinity (Côté et al., 1998; Moreira and Holmberg, 1999; Quinn et al., 1996). SWI/SNF
binding properties are similar to high mobility group (HMG)-box containing proteins which
recognize structured DNA without sequence specificity in a DNA length dependent manner
(Côté et al., 1998; Grosschedl et al., 1994; Pil et al., 1993; Quinn et al., 1996).
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