Transcription regulator. Forms a sequence-specific DNA-binding protein complex with MAD1, MAD4, MNT, WBSCR14 and MLXIP which recognizes the core sequence 5'-CACGTG-3'. The TCFL4-MAD1, TCFL4-MAD4, TCFL4-WBSCR14 complexes are transcriptional repressors. Plays a role in transcriptional activation of glycolytic target genes. Involved in glucose-responsive gene regulation. Efficient DNA binding requires dimerization with another bHLH protein. Binds DNA as a heterodimer with MAD1, MAD4, MNT, WBSCR14 and MLXIP. Can also bind DNA as a homodimer. Found predominantly in the cytoplasm (PubMed:10918583). Found predominantly in the cytoplasm (PubMed:10918583). Found predominantly in the nucleus (PubMed:10918583). Expressed in all tissues tested, including spleen, thymus, prostate, ovary, intestine, colon, peripheral blood leukocyte, heart, liver, skeletal muscle and kidney. Lower levels of expression in testis, brain, placenta and lung.