Communication between distinct subunit interfaces of the cohesin complex promotes its topological entrapment of DNA

Abstract

Cohesin mediates higher-order chromosome structure. Its biological activities require 9 topological entrapment of DNA within a lumen(s) formed by cohesin subunits. The 10 reversible dissociation of cohesin's Smc3p and Mcd1p subunits are postulated to form a 11 regulated gate that allows DNA entry and exit into the lumen. We assessed gate-12 independent functions of this interface in yeast using a fusion protein that joins Smc3p to 13Mcd1p. We show that in vivo all the regulators of cohesin promote DNA binding of 14 cohesion by mechanisms independent of opening this gate. Furthermore, we show that 15 this interface has a gate-independent activity essential for cohesin to bind chromosomes. 16We propose this interface regulates DNA entrapment by controlling the opening and 17closing of one or more distal interfaces formed by cohesin subunits, likely by inducing a 18 conformation change in cohesin. Furthermore, cohesin regulators modulate the interface 19to control both DNA entrapment and cohesin functions after DNA binding. 20 21 the two head domains at the other ( Figure 1A). A smaller lumen is formed by the 46 binding of the Mcd1p C-terminal domain to the Smc1p head domain, and the binding of 47 K112 K113 head domain residues promotes stable cohesin DNA binding and cohesion 69

A Structure-Based Mechanism for DNA Entry into the Cohesin Ring

“…However, the Smc3-kleisin fusion in itself will not block operation of the kleisin N-gate or subsequent DNA passage through the head gate. Indeed, a functional kleisin N-gate remains required for the viability of Smc3-kleisin fusion strains (Guacci et al, 2019). We therefore suggest that the fusion does not impede the loading reaction but, rather, results in a loading product in which the linker sequence between Smc3 and the kleisin adds an additional DNA embrace.…”

Scc2 counteracts a Wapl-independent mechanism that releases cohesin from chromosomes during G1

“…We therefore tested whether cohesin containing a Smc3-Scc1 fusion protein, which restores viability to eco1Δ cells by inactivating Wapl-dependent release, persists on chromosomes upon Scc2 inactivation in late G1 cells. Association with chromosomes of the Smc3-Scc1 fusion protein depends on Scc2 (Guacci et al, 2019). Moreover, Scc2 inactivation does not affect the stability of the fusion protein (Figure 4—figure supplement 1E).…”