Since they lack a putative transactivation domain, the small Mafs behave as transcriptional repressors when they dimerize among themselves (By similarity). However, they act as transcriptional activators by dimerizing with other (usually larger) basic-zipper proteins, such as NFE2, NFE2L1/NRF1, NFE2L2/NRF2 and NFE2L3/NRF3, and recruiting them to specific DNA-binding sites (PubMed:9240432). Small Maf proteins heterodimerize with Fos and may act as competitive repressors of the NF-E2 transcription factor (By similarity). Homodimer or heterodimer (By similarity). It can form high affinity heterodimers with members of the CNC-bZIP family such as NFE2, NFE2L1/NRF1, NFE2L2/NRF2 and NFE2L3/NRF3 (PubMed:9240432). Highly expressed in heart, skeletal muscle and placenta. Also expressed in erythroid cells. Belongs to the bZIP family. Maf subfamily.