Enables DNA-binding transcription activator activity, RNA polymerase II-specific; RNA polymerase II transcription regulatory region sequence-specific DNA binding activity; and identical protein binding activity. Involved in cellular response to glucose starvation; endoplasmic reticulum unfolded protein response; and negative regulation of myotube differentiation. Acts upstream of or within several processes, including glucose homeostasis; intracellular distribution of mitochondria; and mitochondrial calcium ion transmembrane transport. Located in nucleus. Is expressed in alimentary system; early conceptus; genitourinary system; and limb mesenchyme. Orthologous to human BHLHA15 (basic helix-loop-helix family member a15). [provided by Alliance of Genome Resources, Apr 2022]