The promoter region of insulin gene. The organization of the proximal portion (-340 bp to +1 bp) of the insulin promoter including critical transcription activation elements and their binding transcription factors are shown. The critical transcription activation elements are illustrated as boxes. Above the boxes are shown the names of transcription factors that can bind to corresponding elements. Elements A3, C1, E1 have been implicated in β cell-specific expression of the insulin gene, which is mediated by the restricted cellular distribution of their transcription factors PDX-1, MafA, Beta-2. The synergistic activities of PDX-1, MafA and Beta-2 are illustrated by green arrows. In addition to transcription factors, DNA-binding proteins such as HMG I (Y) can promote the binding of PDX-1 and Beta2/E47 to their corresponding elements.