Mitotic and meiotic cohesin complexes in Drosophila melanogaster

Cohesin is a ring-shaped SMC complex that holds sister chromatids together from DNA replication until anaphase and also organizes interphase chromatin into loops. The ring is built from the SMC1-SMC3 heterodimer, whose ATPase heads are bridged by a kleisin subunit, which in turn binds a stromalin (SA) subunit. In mitotic cells the kleisin is Rad21, encoded in Drosophila by verthandi (vtd), and the SA subunit is SA1; separase cleavage of Rad21 opens the ring at anaphase. Drosophila meiosis uses meiosis-specific cohesion proteins: C(2)M, a kleisin-family protein required for synaptonemal complex formation, and Solo and Sunn, which are required for meiotic centromeric cohesion.

The three FlyBase groups (COHSN, COHSN-SOLO-SUNN, COHSN-C2M-SA) share SMC1 and SMC3, which are modelled once as the core part; the variant-specific subunits form a variant set. The meiotic complex term is placed on the meiotic variant nodes even though each node lists only its non-SMC subunits. Cohesin loaders (Nipped-B, Mau-2), Pds5, Wapl, separase and shugoshin (MEI-S332) are regulators outside the module. The SMC subunits are given ATP hydrolysis activity (GO:0016887), which they carry in GOA (ISS, NAS, IEA); their ATPase heads, engaged across the heterodimer, drive the complex. GO has a complex-level term for SMC-complex DNA entrapment (GO:0061776 ATP-dependent topological DNA co-entrapment activity, used by PomBase for the fission yeast complexes), but it is not annotated to the Drosophila proteins and is not asserted here. FlyBase groups realized by this module: COHSN (FBgg0000156), COHSN-SOLO-SUNN (FBgg0001799), COHSN-C2M-SA (FBgg0001800). Participants were generated from the FlyBase gene-group membership and mapped to UniProtKB by projects/FLYBASE_GENE_GROUPS/generate_modules.py from module_specs/dmel_cohesin_complexes.yaml. None of the member genes has a gene review in this repository yet.