Substrate-recognition component of the SCF(FBXL3) E3 ubiquitin ligase complex involved in circadian rhythm function. Plays a key role in the maintenance of both the speed and the robustness of the circadian clock oscillation (PubMed:17463251, PubMed:23452855, PubMed:27565346). The SCF(FBXL3) complex mainly acts in the nucleus and mediates ubiquitination and subsequent degradation of CRY1 and CRY2 (PubMed:17463251, PubMed:23452855, PubMed:27565346). Activity of the SCF(FBXL3) complex is counteracted by the SCF(FBXL21) complex (PubMed:23452855).