THE WORLD ACCORDING TO MAF

Maf family proteins are so named because of their structural similarit y to the founding member, the oncoprotein v-Maf, The small Maf protein s (MafF, MafG and MafK), as do all family members, include a character istic basic region linked to a leucine zipper (b-Zip) domain which med iate DNA binding and subunit dimerization respectively, The small Maf proteins form homodimers or heterodimers with other b-Zip proteins pre sent in the cell and bind to Maf recognition elements (MARE) in DNA, S ince they lack known transcriptional activation domains, the small Maf proteins function either as obligatory heterodimeric partner molecule s with numerous large subunits, discussed below, or alternatively as h omo- or heterodimeric transcriptional repressors. The three small Maf proteins are expressed in a number of overlapping tissues, but their e xpression profiles nonetheless appear to be under meticulous tissue- a nd developmental stage-specific control, The MARE bears a striking res emblance to the NF-E2 binding sequence, NF-E2 binding sites in the hum an beta-globin locus control region have been directly implicated as i ntegral components in the circuitry required for eliciting changes in chromatin structure that precede globin gene activation, While the NF- E2 DNA sequence has been shown to be important for erythroid-specific gene regulation, a growing list of other genes may also be regulated t hrough the same, or very similar, cis elements in non-erythroid cells, Taken together, these observations argue that comprehensive analysis of the activities of the small Maf proteins may provide a unique persp ective for expanding our understanding of transcriptional regulation t hat can be elicited through interacting transcription factor networks.