The structure of this protein repressor, which is the shortest reported to date and the first isolated from a plasmid, has a homodimeric ribbon-helix-helix arrangement [2]. The helix-turn-helix-like structure is involved in dimerisation and not DNA binding as might have been expected [2].

1: Structural features of the plasmid pMV158-encoded transcriptional repressor CopG, a protein sharing similarities with both helix-turn-helix and beta-sheet DNA binding proteins. Acebo P, Garcia de Lacoba M, Rivas G, Andreu JM, Espinosa M, del Solar G Proteins 1998;32:248-261. PMID:9714164

2: The structure of plasmid-encoded transcriptional repressor CopG unliganded and bound to its operator. Gomis-R th FX, Sol M, Acebo P, Parraga A, Guasch A, Eritja R, Gonzalez A, Espinosa M, del Solar G, Coll M EMBO J 1998;17:7404-7415. PMID:9857196