Human small Maf proteins form heterodimers with CNC family transcription factors and recognize the NF-E2 motif

The transcription factor NF-E2. a heterodimeric protein complex composed of p45 and small Maf family proteins, is considered crucial for the regulatio n of erythroid gene expression and platelet formation. To facilitate the ch aracterization of NF-E2 functions in human cells, we isolated cDNAs encodin g two members of the small Maf family MafK and MafG. The human MafK and Maf G genes encode proteins of 156 and 162 amino acid residues, respectively, w hose deduced amino acid sequences show approximately 95% identity to their respective chicken counterparts. Both are expressed in all hematopoietic ce ll lines, including those of erythroid and megakaryocytic lineages. In elec trophoretic gel mobility shift assays binding to NF-E2 sites were found to depend on formation of homodimers or heterodimers with p45 and p45-related CNC family proteins and transient transfection assays in COS-I cells confir med that these heterodimers regulate transcription through NF-E2 sites. Fur thermore, a novel member of CNC family proteins Bach1 was found to be invol ved in transcriptional regulation through NF-E2 site. The results suggest t hat the small Maf family proteins function in human cells through interacti on with various basic leucine zipper-type transcription factors.