Members of this family are involved in the repression of transcription by binding as a homodimer to palindromic DNA operator sites in phage lambda: they repress genes expressed in early phage development and are necessary for the late stage of lytic growth. These proteins have a secondary structure consisting of three alpha-helices and three beta-sheets, and dimerise through interactions between the two antiparallel beta-strands [1].

1: The structural basis for enhanced stability and reduced DNA binding seen in engineered second-generation Cro monomers and dimers. Rupert PB, Mollah AK, Mossing MC, Matthews BW; J Mol Biol. 2000;296:1079-1090. PMID:10686105