Enables ubiquitin protein ligase activity. Involved in regulation of circadian rhythm and ubiquitin-dependent protein catabolic process. Predicted to be located in several cellular components, including early endosome; neuronal cell body; and nucleoplasm. Predicted to be active in cytoplasm. Is expressed in several structures, including brain; cranium; gonad; hemolymphoid system gland; and sensory organ. Orthologous to human SIAH2 (siah E3 ubiquitin protein ligase 2). [provided by Alliance of Genome Resources, Apr 2022]