the closest homologue to "fbxl3" is "fbxl21" as it also binds to the cry1 and cry2 proteins. predominantly localized to the cytosol, "fbxl21" has been proposed to antagonize the action of "fbxl3" through ubiquitination and stabilization of cry proteins instead of leading it to degradation. fbxl21 is expressed predominantly in the suprachiasmatic nucleus, which is the region in the brain that functions as the master pacemaker in mammals.