Since they lack a putative transactivation domain, the small Mafs behave as transcriptional repressors when they dimerize among themselves (PubMed:11154691). 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 (PubMed:8932385, PubMed:9421508, PubMed:11154691). Small Maf proteins heterodimerize with Fos and may act as competitive repressors of the NFE2L2 transcription factor (PubMed:11154691). Transcription factor, component of erythroid-specific transcription factor NFE2L2 (PubMed:11154691). Activates globin gene expression when associated with NFE2L2 (PubMed:11154691). 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 (PubMed:8932385, PubMed:9421508, PubMed:11154691). Interacts with CREBBP; the interaction leads to acetylation of the basic region of MAFG and stimulation of NFE2 transcriptional activity through increased DNA binding. Highly expressed in skeletal muscle. Also expressed in heart and brain. 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.