The SMC/Rad50/RecN proteins are universal DNA‐associated ABC‐type ATPases with crucial functions in genome maintenance. New insights into Rad50–DNA complex structure and cohesin regulation inspire a speculative look at the entire superfamily. Identification of a continuous DNA binding site across the Rad50 dimer interface (Liu et al, 2016; Seifert et al, 2016) suggests a similar site in cohesin. The localization of this site hints a DNA‐activated mechanism for cohesin removal from chromosomes.
See also: Y Liu et al (April 2016) and
FU Seifert et al (April 2016)
The Smc proteins form the core of multi‐subunit complexes that are essential for genome stability. The cohesin complex is needed for sister chromatid cohesion and is built around heterodimers of Smc1 and Smc3, while the MRN (Mre11–Rad50–Nbs1) DNA repair complex contains homodimers of the Smc protein Rad50. The large and elongated Smc proteins have Walker A and B motifs at their globular ends, and are folded on themselves at a central hinge domain (called hook in Rad50). This leads to the formation of an ATPase‐containing head which is connected to the hinge through an antiparallel coiled coil. Within the complex, the Smc proteins bind each other at the hinge/hook, and two ATP molecules are sandwiched between their heads. The heads are also sites for interactions with additional subunits of the complexes, such as the nuclease Mre11 in MRN, and Scc1 in cohesin (Fig 1A and B).
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