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 NFE2, NFE2L1 and NFE2L2, and recruiting them to specific DNA-binding sites. Small Maf proteins heterodimerize with Fos and may act as competitive repressors of the NFE2L2 transcription factor. Transcription factor, component of erythroid-specific transcription factor NFE2L2. Activates globin gene expression when associated with NFE2L2 (By similarity). May be involved in signal transduction of extracellular H(+) (By similarity). Homodimer or heterodimer. Homodimerization leads to transcriptional repression. Forms high affinity heterodimers with members of the CNC-bZIP family such as NFE2, NFE2L1/NRF1, NFE2L2/NRF2 and NFE2L3/NRF3. Interacts with CREBBP; the interaction leads to acetylation of the basic region of MAFG and stimulation of NFE2 transcriptional activity through increased DNA binding. Acetylated in erythroid cells by CREB-binding protein (CBP). Acetylation augments the DNA-binding activity of NFE2, but has no effect on binding NFE2. Sumoylation at Lys-14 is required for active transcriptional repression. Belongs to the bZIP family. Maf subfamily.