May control regulatory pathways relevant to schizophrenia and to psychotic illness. May play a role in late central nervous system development by modulating EPO expression in response to cellular oxygen level (By similarity). Forms a heterodimer that binds core DNA sequence 5'-TACGTG-3' within the hypoxia response element (HRE) leading to transcriptional repression on its target gene TH (By similarity). Efficient DNA binding requires dimerization with another bHLH protein. Interacts with ARNT; forms a heterodimer that binds core DNA sequence 5'-[AG]CGTG-3' within the hypoxia response element (HRE) leading to a transcriptional repressor on its target gene TH (By similarity).