An SMC-like protein binds and regulates Caenorhabditis elegans condensins

Structural maintenance of chromosomes (smc) family proteins participate in multisubunit complexes that govern chromosome structure and dynamics. smc-containing condensin complexes create chromosome topologies essential for mitosis/meiosis,gene expression,recombination,and repair. many eukaryotes have two condensin complexes (i and ii); c. elegans has three (i,ii,and the x-chromosome specialized condensin idc) and their regulation is poorly understood. here we identify a novel smc-like protein,smcl-1,that binds to c. elegans condensin smc subunits,and modulates condensin functions. consistent with a possible role as a negative regulator,loss of smcl-1 partially rescued the lethal and sterile phenotypes of a hypomorphic condensin mutant,while over-expression of smcl-1 caused lethality,chromosome mis-segregation,and disruption of condensin idclocalization on x chromosomes. unlike canonical smc proteins,smcl-1 lacks hinge and coil domains,and its atpase domain lacks conserved amino acids required for atp hydrolysis,leading to the speculation that it may inhibit condensin atpase activity. smcl-1 homologs are apparent only in the subset of caenorhabditis species in which the condensin i and ii subunit smc-4 duplicated to create the condensin idc- specific subunit dpy-27,suggesting that smcl-1 helps this lineage cope with the regulatory challenges imposed by evolution of a third condensin complex. our findings uncover a new regulator of condensins and highlight how the duplication and divergence of smc complex components in various lineages has created new proteins with diverse functions in chromosome dynamics. © 2017 chao et al.