SCC1MCD1

Scc1Mcd1 is a highly conserved protein that functions as a core subunit of the cohesin complex, which is essential for sister chromatid cohesion during cell division. In the budding yeast Saccharomyces cerevisiae, the gene encoding this protein is known as mcd1 (for “maintenance of chromosome integrity”). The protein is named Scc1 in Schizosaccharomyces pombe, reflecting its orthologous role across eukaryotes.

Structurally, Scc1Mcd1 contains a long coiled‑coil domain followed by a short C‑terminal domain that binds to the ATPase heads of the Smc1 and Smc3 subunits of cohesin. This architecture facilitates the formation of a tripartite ring that topologically entraps DNA strands. Post‑translational modifications, such as acetylation by the Eco1 acetyltransferase during the S phase, stabilize the ring and promote loading onto chromatin.

During the mitotic cycle, Scc1Mcd1 is loaded onto chromatin by the Scc2/Scc4 loader complex and is resistant to removal by the AAA+ ATPase Wapl until the onset of anaphase, when cleavage by separase releases the sister chromatids. In addition to cohesion, the cohesin complex, with Scc1Mcd1 as a central component, participates in DNA repair, transcription regulation, and the maintenance of higher‑order chromatin architecture.

Mutations in SCC1/MCD1 are lethal in yeast and are associated with cohesion defects. In humans, the homologous protein RAD21 (which is also referred to as Scc1) is implicated in cleavage‑channelling and, when mutated, can contribute to developmental disorders such as Cornelia de Lange syndrome. The study of Scc1Mcd1 therefore provides insight into fundamental mechanisms of chromosome biology applicable to a wide range of organisms.