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. {ECO:0000269|PubMed:10593926, ECO:0000269|PubMed:12446771, ECO:0000269|PubMed:16782875}. This is the function of Ensembl gene identifier ENSG00000108788 (MLX, MAX dimerization protein MLX).