The developmentally regulated expression of the globin genes depends on upstream regulatory elements termed locus control regions (LCRs). LCRs are associated with powerful enhancer activity that is mediated by the transcription factor NFE2 (nuclear factor erythroid-2). NFE2 recognition sites are also present in the gene promoters of 2 heme biosynthetic enzymes, porphobilinogen deaminase (PBGD; MIM 609806) and ferrochelatase (FECH; MIM 612386). NFE2 DNA-binding activity consists of a heterodimer containing an 18-kD Maf protein (MafF, MafG (MIM 602020), or MafK) and p45 (MIM 601490). Both subunits are members of the activator protein-1 superfamily of basic leucine zipper (bZIP) proteins (see MIM 165160). Maf homodimers suppress transcription at NFE2 sites.[supplied by OMIM, Nov 2008].