A handcuff model for the cohesin complex

Abstract

The cohesin complex is responsible for the accurate separation of sister chromatids into two daughter cells. Several models for the cohesin complex have been proposed, but the one-ring embrace model currently predominates the fi eld. However, the static confi guration of the embrace model is not fl exible enough for cohesins to perform their functions during DNA replication, transcription, and DNA repair. We used coimmunoprecipitation, a protein fragment complement assay, and a yeast two-hybrid assay to analyze the protein - protein interactions among cohesin subunits. The results show that three of the four human cohesin core subunits (Smc1, Smc3, and Rad21) interact with themselves in an Scc3 (SA1/ SA2)-dependent manner. These data support a two-ring handcuff model for the cohesin complex, which is fl exible enough to establish and maintain sister chromatid cohesion as well as ensure the fi delity of chromosome segregation in higher eukaryotes. © 2008 Zhang et al.