Snf2 subfamily
The archetype of the Snf2 subfamily, and the entire
Snf2 family, is the S cerevisiae Snf2 protein,
originally identified genetically because of its role
in sugar metabolism (Sucrose Non Fermentation, SNF2)
1, 2 and mating type
SWItching (SWI2) 3.
However, these genes were subsequently found to play
roles in the regulation of transcription a broader
spectrum of genes 4. The link between
the function of this complex and chromatin came when
Snf2 suppressor mutations were identified in yeast
histone genes 5.
Subsequently the proteins were purified and found to
form an 11 subunit multi-protein complex capable of
ATP-dependent chromatin disruption and termed the
SWI/SNF complex 6, 7, 8.
Although Snf2p deletions are viable under certain
conditions and affect transcription of only a fraction
of all yeast genes during growth under standard
laboratory conditions 9, 10, its close
homologue Sth1p which forms the core of the RSC
complex is essential 11, 7.
Close sequence homologues in a Snf2 subfamily have
also been identified and studied in many model
organisms, including the D melanogaster Brahma 12 and human hBRM
13 and BRG1 14 proteins. Many of
these have been shown to alter the structure of
chromatin at the nucleosomal level and to be
involved in transcription regulation, although other
nucleosome related roles have also been identified
15.
Recent hypotheses have centred on Snf2 subfamily
members performing a generally disruptive function on
nucleosomes leading either to sliding of the nucleosome
16, 17 or to partial or
complete removal of the histone octamer components
18, 19.
Homologues of Snf2p, such as BRG1 and hBRM have been
identified as components of megadalton size complexes
containing many proteins that are related to components
of the yeast SWI/SNF complex 20. However, Snf2
subfamily members have also been reported to
interact with additional proteins.
These include histone deacetylases 21, methyl DNA
binding proteins 22, histone methyl
transferases 23, the
retinoblastoma tumor suppressor protein 24, 25, histone
chaperones 26, Pol II 27, 28, cohesin 29. These complexes
may be recruited to specific regions of the genome
through interactions with sequence specific DNA
binding proteins (reviewed by 30) or specific
patterns of histone modifications 31, 32.
names associated with subfamily members
Snf2p, Sth1p, snf21, SMARCA4, BRG1, BAF190,
hSNF2beta, SNF2L4, SMARCA2, hBRM, hSNF2a, SNF2L2,
SNF2LA, SYD, splayed, psa-4, brahma
references
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