Acts as a transcriptional activator or repressor. Plays a pivotal role in regulating lineage-specific hematopoiesis by repressing ETS1-mediated transcription of erythroid-specific genes in myeloid cells. Required for monocytic, macrophage, osteoclast, podocyte and islet beta cell differentiation. Involved in renal tubule survival and F4/80 maturation. Activates the insulin and glucagon promoters. Together with PAX6, transactivates weakly the glucagon gene promoter through the G1 element. SUMO modification controls its transcriptional activity and ability to specify macrophage fate. Binds element G1 on the glucagon promoter. Involved either as an oncogene or as a tumor suppressor, depending on the cell context (By similarity). Required for the transcriptional activation of HOXB3 in the rhombomere r5 in the hindbrain (By similarity). Homodimer or heterodimer with other bHLH-Zip transcription factors. Forms homodimers and heterodimers with FOS, FOSB and FOSL2, but not with JUN proteins (JUN, JUNB and JUND). Binds DNA as a homodimer or a heterodimer. Interacts with the intracellular cytoplasmic domain of LRP1 (LRPICD); the interaction results in a moderate reduction of MAFB transcriptional potential. Interacts with PAX6; the interaction is direct. Interacts with ETS1 and LRP1 (By similarity). Expressed at low levels in a variety of tissues, including liver, muscle and spleen. Strongly expressed in hypertrophic chondrocytes of the femur epiphysis, while expression is very weak in immature proliferating chondrocytes (at protein level). Expressed in the cartilage of ribs and limbs, in the eyes and spinal cord at 15 dpc (at protein level). Expressed in the lens epithelium at 13 and 16 dpc; not detected in the fiber cells of the lens. In the eyes, confined in the equator of the lens; not detected in the retina at 15 dpc. In spinal cord, expressed in the ventral part of the dorsal horn and the ventral horn at 15 dpc. Predominantly expressed in postmitotic cells. The leucine-zipper domain is involved in the interaction with LRPICD. Sumoylated. Sumoylation on Lys-32 and Lys-297 stimulates its transcriptional repression activity and promotes macrophage differentiation from myeloid progenitors (By similarity). Belongs to the bZIP family. Maf subfamily.