STAG1

Cohesin subunit SA-1 (SA1) is a protein that in humans is encoded by the STAG1 gene.^[5][6] SA1 is a subunit of the Cohesin complex which mediates sister chromatid cohesion, homologous recombination and DNA looping. In somatic cells cohesin is formed of SMC3, SMC1, RAD21 and either SA1 or SA2 whereas in meiosis, cohesin is formed of SMC3, SMC1B, REC8 and SA3. There is a nonprofit community formed for those with a STAG1 Gene mutation at www.stag1gene.org.

STAG1
Identifiers
Aliases	STAG1, SA1, SCC3A, stromal antigen 1, MRD47
External IDs	OMIM: 604358; MGI: 1098658; HomoloGene: 21191; GeneCards: STAG1; OMA:STAG1 - orthologs
Gene location (Human) Chr. Chromosome 3 (human)[1] Band 3q22.3 Start 136,336,236 bp[1] End 136,752,403 bp[1]
Gene location (Mouse) Chr. Chromosome 9 (mouse)[2] Band 9|9 E3.3- E4 Start 100,479,851 bp[2] End 100,841,428 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in Achilles tendon parotid gland sural nerve ventricular zone synovial joint Skeletal muscle tissue of rectus abdominis tail of epididymis ganglionic eminence pericardium superficial temporal artery Top expressed in tail of embryo genital tubercle ureter ventricular zone Gonadal ridge medial ganglionic eminence cumulus cell spermatocyte abdominal wall maxillary prominence More reference expression data BioGPS More reference expression data
Gene ontology Molecular function DNA-binding transcription activator activity, RNA polymerase II-specific chromatin binding protein binding Cellular component chromosome cytosol chromatin chromosome, centromeric region nucleus nucleoplasm nuclear body cohesin complex nuclear matrix mitotic spindle pole Biological process chromosome segregation cell division cell cycle transcription by RNA polymerase II positive regulation of transcription by RNA polymerase II regulation of mitotic spindle assembly sister chromatid cohesion Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 10274 20842 Ensembl ENSG00000118007 ENSMUSG00000037286 UniProt Q8WVM7 Q9D3E6 RefSeq (mRNA) NM_005862 NM_009282 NM_001357264 NM_001357265 RefSeq (protein) NP_005853 NP_033308 NP_001344193 NP_001344194 Location (UCSC) Chr 3: 136.34 – 136.75 Mb Chr 9: 100.48 – 100.84 Mb PubMed search [3] [4]
Wikidata
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Structure

Structure of SA2 (blue) and RAD21 (green) (PDB 4PK7)

SA1 is one of three human homologues of the yeast protein Scc3 which is a core subunit of the cohesin complex (the three human paralogues are SA1, SA2 and SA3). SA1 and SA2 are expressed in somatic cells whereas SA3 is the main SA paralogue in meiotic cells. In humans, SA2 has been shown to be more abundant than SA1; however, in other cell types, SA1 is the dominant form.^[7]

SA1 stably binds to cohesin via the RAD21 subunit and functions as a platform for other regulatory subunits. The sequences of SA1 and SA2 are 75% conserved. They demonstrate a distinction between the N-terminal region and the C-terminal region.^[8] SA1 has an evident AT-hook at the N-terminal region.^[9]

Function

SA1 has roles in regulating both cohesin loading and release.^[6] SA1 functions specifically in telomere cohesion.^[10]

In mice, SA1 is required for embryonic development and has been shown to be lethal if not expressed.^[11]