Predicted to enable DNA-binding transcription factor activity, RNA polymerase II-specific and RNA polymerase II cis-regulatory region sequence-specific DNA binding activity. Acts upstream of or within negative regulation of DNA-templated transcription; response to cold; and sleep. Predicted to be active in nucleus. Is expressed in several structures, including brain; cardinal system; pleuroperitoneal region; shield; and swim bladder bud. Orthologous to human BHLHE41 (basic helix-loop-helix family member e41).