May be a component of the 9-1-1 cell-cycle checkpoint response complex that plays a major role in DNA repair. Putative component of the toroidal 9-1-1 (RAD9-RAD1-HUS1) complex, composed of hpr-9, mrt-2 and hus-1 (Probable). RNAi-mediated knockdown disrupts hus-1 localization to the nucleus. Belongs to the rad9 family.