Gene Regulation by HMGA and HMGB Chromosomal Proteins and Related Architectural DNA-Binding Proteins

The eukaryotic abundant high mobility group HMGA and HMGB proteins can act as architectural transcription factors by promoting the assembly of higher-order protein-DNA complexes which can either activate or repress gene expression. The structural organisation of both classes of protein is similar with either a single or repeated DNA binding domain preceding a short negatively charged C-terminal tail. In the HMGB class of proteins the HMG DNA-binding domain binds non-specifically and introduces a sharp bend into DNA whereas the AT-hook in the HMGA protein binds preferentially to A/T rich regions of DNA and stabilises a B-DNA structure. The acidic tails are hypothesised to facilitate the interaction of the proteins with nudeosomes by binding to the positively charged histone tails. Both classes of protein also interact with a large number of transcription factors that bind to specific DNA sequences.