Since they lack a putative transactivation domain, the small Mafs behave as transcriptional repressors when they dimerize among themselves. However, they seem to serve as transcriptional activators by dimerizing with other (usually larger) basic-zipper proteins, such as NFE2L1/NRF1, and recruiting them to specific DNA-binding sites. Interacts with the upstream promoter region of the oxytocin receptor gene. May be a transcriptional enhancer in the up-regulation of the oxytocin receptor gene at parturition. Monomer and homo- or heterodimer. Interacts with MIP. Forms high affinity heterodimers with members of the CNC-bZIP family such as NFE2L1/NRF1. Highly expressed in the lung, lower expression in the brain, thymus, liver, spleen, intestine, kidney, heart, muscle, and ovary. Not significantly expressed in hematopoietic cells. Detected at 6.5 dpc in the boundary between the extraembryonic and embryonic regions. At 8.5 dpc, weakly expressed in the future gut, allantois, yolk sac endoderm and the ectoplacental cone. At 9.5 dpc, strong expression in the primordial gut and presumptive fetal liver, in the floorplate of the myelencephalon, neural crest cells, spongiotrophoblasts, and giant cells of the placenta. At 12.5 dpc, detected in hepotocytes, in the outflow tract of the heart in a specific subset of dorsal root ganglia, in the cranial nerve ganglia, in the lung primordium, and in the epithelium of the expiratory tract. In newborn, strongly expressed in keratinocytes, in the cartilage, in bronchial epithelia, and bone membrane. Belongs to the bZIP family. Maf subfamily.