A Conserved Domain in the Scc3 Subunit of Cohesin Mediates the Interaction with Both Mcd1 and the Cohesin Loader Complex

Abstract

The Structural Maintenance of Chromosome (SMC) complex, termed cohesin, is essential for sister chromatid cohesion. Cohesin is also important for chromosome condensation, DNA repair, and gene expression. Cohesin is comprised of Scc3, Mcd1, Smc1, and Smc3. Scc3 also binds Pds5 and Wpl1, cohesin-associated proteins that regulate cohesin function, and to the Scc2/4 cohesin loader. We mutagenized SCC3 to elucidate its role in cohesin function. A 5 amino acid insertion after Scc3 residue I358, or a missense mutation of residue D373 in the adjacent stromalin conservative domain (SCD) induce inviability and defects in both cohesion and cohesin binding to chromosomes. The I358 and D373 mutants abrogate Scc3 binding to Mcd1. These results define an Scc3 region extending from I358 through the SCD required for binding Mcd1, cohesin localization to chromosomes and cohesion. Scc3 binding to the cohesin loader, Pds5 and Wpl1 are unaffected in I358 mutant and the loader still binds the cohesin core trimer (Mcd1, Smc1 and Smc3). Thus, Scc3 plays a critical role in cohesin binding to chromosomes and cohesion at a step distinct from loader binding to the cohesin trimer. We show that residues Y371 and K372 within the SCD are critical for viability and chromosome condensation but dispensable for cohesion. However, scc3 Y371A and scc3 K372A bind normally to Mcd1. These alleles also provide evidence that Scc3 has distinct mechanisms of cohesin loading to different loci. The cohesion-competence, condensation-incompetence of Y371 and K372 mutants suggests that cohesin has at least one activity required specifically for condensation.

Pds5 regulators segregate cohesion and condensation pathways in Saccharomyces cerevisiae

“…The current study thus reveals that the pathways of condensation and cohesion can be separated and that the critical role of Pds5 is biased toward maintaining sister chromatid cohesion. During final revision of the current manuscript, Orgil and colleagues identified IRR1/ SCC3 separation of function alleles that provide further insight into cohesion roles (47). These tools will be critical in assessing how regulatory factors direct cohesin modifications and structures toward cohesion, condensation, and transcription (13).…”

Monomeric cohesin state revealed by live‐cell single‐molecule spectroscopy

“…Cohesin cannot be established in the absence of Scc3 or Eco1 [9,16,[32][33][34]. Intriguingly, depletion of Scc3 resulted in slower diffusion of Scc1-GFP at all stages of the cell cycle.…”

The Arabidopsis homolog of Scc4/MAU2 is essential for embryogenesis

“…The V-like structure is closed by the simultaneous binding of the N-and C-terminal regions of the kleisin (Scc2, Rec8) to the head domains of SMC3 and SMC1, respectively Nasmyth and Haering, 2005). The stromalin (Scc3) subunit of the cohesin complex binds the kleisin subunit to facilitate interaction between cohesin ring and its regulating complexes (Orgil et al, 2015). The NIBPL (Scc2) subunit of the cohesin-loading complex interacts directly with Scc3 and is sufficient for loading of cohesin rings on DNA in vitro.…”