Homology among DNA-binding proteins suggests use of a conserved super-secondary structure

Abstract
The amino acid sequences of the repressor and cro proteins of phages λ, 434 and P22 are homologous, especially in a region in which repressor and λ cro have a similar α-helix–turn–α-helix secondary structure. Model-building studies indicate that this structure is important in DNA binding, and we suggest it may be a common feature of many DNA-binding proteins.