Transcription factor that activates insulin gene expression (PubMed:12011435, PubMed:15993959). Acts synergistically with NEUROD1/BETA2 and PDX1 (PubMed:15993959). Binds the insulin enhancer C1/RIPE3b element (PubMed:12011435). Binds to consensus TRE-type MARE 5'-TGCTGACTCAGCA-3' DNA sequence (PubMed:23148532, PubMed:29339498). {ECO:0000269|PubMed:12011435, ECO:0000269|PubMed:15993959, ECO:0000269|PubMed:23148532, ECO:0000269|PubMed:29339498}. This is the function of MAFA (MAF bZIP transcription factor A, Ensembl gene identifier ENSG00000182759).