Transcription factor MafK is a bZip Maf transcription factor protein that in humans is encoded by the MAFK gene. MafK is one of the small Maf proteins, which are basic region and leucine zipper (bZIP)-type transcription factors. The HUGO Gene Nomenclature Committee-approved gene name of MAFK is “v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog K”. Discovery MafK was first cloned and identified in chicken in 1993 as a member of the small Maf (sMaf) genes. MafK was also identified as p18 NF-E2, a component of NF-E2 complex binding to a specific motif (NF-E2) in the regulatory regions of β-globin and other erythroid-related genes. MAFK has been identified in many vertebrates, including humans. There are three functionally redundant sMaf proteins in vertebrates, MafF, MafG, and MafK. Structure MafK has a bZIP structure that consists of a basic region for DNA binding and a leucine zipper structure for dimer formation. Similar to other sMafs, MafK lacks any canonical transcriptional activation domains. Expression MAFK is broadly but differentially expressed in various tissues. MAFK expression was detected in all 16 tissues examined by the human BodyMap Project, but relatively abundant in adipose, lung and skeletal muscle tissues. Mouse Mafk is regulated by different GATA factors in both hematopoietic and cardiac tissues. MAFK expression is influenced by TGF-β and Wnt signaling, and rat Mafk expression is influenced by NGF and AKT in neuronal cells. Function Because of sequence similarity, no functional differences have been observed among the sMafs in terms of their bZIP structures. sMafs form homodimers by themselves and heterodimers with other specific bZIP transcription factors, such as CNC (cap 'n' collar) proteins [p45 NF-E2 (NFE2), Nrf1 (NFE2L1), Nrf2 (NFE2L2), and Nrf3 (NFE2L3)] and Bach proteins (BACH1 and BACH2). sMaf homodimers bind to a palindromic DNA sequence called the Maf recognition element (MARE: TGCTGACTCAGCA) and its related sequences. Structural analyses have demonstrated that the basic region of a Maf factor recognizes the flanking GC sequences. By contrast, CNC-sMaf or Bach-sMaf heterodimers preferentially bind to DNA sequences (RTGA(C/G)NNNGC: R=A or G) that are slightly different from MARE. The latter DNA sequences have been recognized as antioxidant/electrophile response elements or NF-E2-binding motifs to which Nrf2-sMaf heterodimers and p45 NF-E2-sMaf heterodimer bind, respectively. It has been proposed that the latter sequences should be classified as CNC-sMaf-binding elements (CsMBEs). It has also been reported that sMafs form heterodimers with other bZIP transcription factors, such as c-Jun and c-Fos. Target