Many gene-regulatory proteins appear to have a similar α-helical fold that binds DNA and evolved from a common precursor

Amino acid and DNA sequence comparisons suggest that many sequence-specific DNA-binding proteins have in common and homologous region of about 22 amino acids. This region corresponds to two consecutive α-helices that occur in bot Cro and cI repressor proteins of bacteriophage λ and in catabolite gene activator protein of Escherichia coli and are presumed to interact with DNA. The results obtained here suggest that this α-helical DNA-binding fold occurs in many proteins that regulate gene expression. It also appears that this DNA-binding unit evolved from a common evolutionary precursor.