Enables protein heterodimerization activity. Involved in negative regulation of transcription, DNA-templated. Acts upstream of or within maternal behavior; negative regulation of transcription by RNA polymerase II; and startle response. Located in nucleus. Is expressed in several structures, including central nervous system; genitourinary system; and limb. Orthologous to human NPAS1 (neuronal PAS domain protein 1). [provided by Alliance of Genome Resources, Apr 2022]