The heterodimer formation of Nrf2 with one of the small Maf (musculoaponeurotic fibrosarcoma) proteins (MafF, MafG, and MafK) is necessary for Nrf2 binding to CsMBE (CNC and small Maf binding element, 5′-(A/G)TGA(G/C)nnnGC) located in promoters or enhancers of Nrf2-target genes (Figure 2) [27]. This evidence concerns the gene NFE2L2 and fibrosarcoma.