SMARCA4 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4)

	Relative size of the 33 coding exons of SMARCA4. The entire exon 1 is UTR (untranslated region). Exon numeration corresponds to the prevalent transcript (matching the EST EU430759).
Description	The SMARCA4 is also known as BRG1 (hSWI/SNF brahma-related gene). It spans a total genomic size of 101347 bp and it is composed of 33 coding exons of varying lengths and 1 non-coding exon (exon 1).
Transcription	The human SMARCA4 transcript has approximately 5500 bp and contains an open reading frame of 4845 bp, predicting a protein of 1614 amino acid residues. There are different transcripts arising from two alternative splicing sites within intron 28 and exon 30, which predict the translation of four different BRG1 protein isoforms. In addition, between exon 26 and 27 and exon 29 and 30 there are two additional exons that may constitute tissue specific transcripts.

	SMARCA4 conserved domains. Proline rich region, containing more than 25% of proline residues in the aminoacid sequence. HSA and BRK domains, containing motifs that may predict binding to DNA. ATPase/helicase domain, contains motifs present in the DEAD helicases superfamily, a diverse family of proteins involved in ATP-dependent RNA or DNA unwinding. Bromodomain, 110 aminoacid domain, found in many chromatin associated proteins. Bromodomains can interact specifically with acetylated lysine.
Description	SMARCA4 has a molecular mass of 181349 Da. SMARCA4 is the catalytic subunit of the chromatin-remodelling complex SWI-SNF and influences transcriptional regulation by disrupting histone-DNA contacts in an ATP-dependent manner. In addition to an ATPase, the SWI/SNF complex is composed of a variety of accessory proteins, termed BAFs (BRG-1-associated factors).
Expression	Widely expressed.
Localisation	SMARCA4 localizes in the nucleus.
Function	The SMARCA4 harbours the ATPase activity required for the chromatin remodelling activity of the SWI/SNF complex. This complex uses the energy of ATP hydrolysis to modify the interactions among histones leading to modifications of the chromatin structure and to the regulation of gene expression. The SWI/SNF complex plays a role in differentiation, development and cell cycle control. SMARCA4 binds to or it is related to important tumor suppressor proteins, including BRCA2, LKB1, RB and FANCA. Moreover, the SWI/SNF complex has been shown to modulate the transcriptional activity of steroid receptors (e.g. glucocorticoids receptors, retinoic acid receptors, androgen and estrogen receptors), CMYC and RB. SMARCA4 acts as a tumor suppressor because: i) it induces cell-growth arrest after ectopic expression in deficient tumor cells; ii) SMARCA4-heterozygous mice have an increased predisposition to tumor development and iii) it is biallelically inactivated by homozygous deletions or combinations of deletions and mutations in several types of tumors, specially in lung cancer.
Homology	The mammalian SWI/SNF complex contains either SMARCA4 or SMARCA2 as its central ATPase subunit. Both ATPases share 80% homology in their aminoacid sequence. However, differences in expression patterns and in the phenotypes of Brm and Brg1 knockout mice suggest specific biological roles between both ATPases. SMARCA2 and SMARCA4 are orthologous to the snf2/swi2 gene from S. cerevisiae and to the "brahma" (brm) gene from Drosophila. These encode proteins that are highly conserved along evolution, especially in the ATPase/helicase domain. Actually, SMARCA2 is 56% identical and 72% homologous to the Drosophila brm.

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