Interallelic complementation provides functional evidence for cohesin-cohesin interactions on DNA

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The cohesin complex is crucial for chromosome architecture, including sister chromatid cohesion, condensation, DNA repair, and gene regulation.
• The prevailing model suggests a single cohesin complex entraps sister chromatids for cohesion.

Purpose of the Study:

• To investigate the mechanism of sister chromatid cohesion mediated by the cohesin complex.
• To explore the functional interactions between cohesin complex components.

Main Methods:

• Utilized interallelic complementation assays with mutant alleles of Mcd1p and Smc3p.
• Assessed cell viability, sister chromatid cohesion, chromosome condensation, and chromosome binding of cohesin components at restrictive temperatures.

Main Results:

• Viability and restoration of cohesion and condensation were observed in cells coexpressing pairs of defective mcd1 or smc3 alleles.
• Individual mutant cohesin proteins (mcd1-1p, smc3-42p) failed to bind chromosomes at restrictive temperatures but regained binding when coexpressed with their complementing partners.
• These results indicate interplay between multiple cohesin complexes.

Conclusions:

• The findings support a model where multiple cohesin complexes interact on DNA to establish and maintain sister chromatid cohesion and chromosome condensation.
• This challenges the prevailing embrace model, suggesting a more complex, cooperative mechanism involving multiple cohesin units.