<p>High mobility group (HMG or HMGB) proteins are a family of relatively low molecular weight non-histone components in chromatin. HMG1 (also called HMG-T in fish) and HMG2 are two highly related proteins that bind single-stranded DNA preferentially and unwind double-stranded DNA. Although they have no sequence specificity, they have a high affinity for bent or distorted DNA, and bend linear DNA. HMG1 and HMG2 contain two DNA-binding HMG-box domains (A and B) that show structural and functional differences, and have a long acidic C-terminal domain rich in aspartic and glutamic acid residues. The acidic tail modulates the affinity of the tandem HMG boxes in HMG1 and 2 for a variety of DNA targets. HMG1 and 2 appear to play important architectural roles in the assembly of nucleoprotein complexes in a variety of biological processes, for example V(D)J recombination, the initiation of transcription, and DNA repair [<cite idref="PUB00015133"/>].</p><p>The profile in this entry describing the HMG-domains is much more general than the signature. In addition to the HMG1 and HMG2 proteins, HMG-domains occur in single or multiple copies in the following protein classes; the SOX family of transcription factors; SRY sex determining region Y protein and related proteins [<cite idref="PUB00015128"/>]; LEF1 lymphoid enhancer binding factor 1 [<cite idref="PUB00015129"/>]; SSRP recombination signal recognition protein; MTF1 mitochondrial transcription factor 1; UBF1/2 nucleolar transcription factors; Abf2 yeast ARS-binding factor [<cite idref="PUB00015130"/>]; and <taxon tax_id="4932">Saccharomyces cerevisiae</taxon> transcription factors Ixr1, Rox1, Nhp6a, Nhp6b and Spp41.</p> High mobility group, HMG1/HMG2