Structural homology between rbs repressor and ribose binding protein implies functional similarity

The deduced amino acid sequence of the rbs repressor, RbsR, of Escherichia coli is homologous over its C-terminal 272 residues to the entire sequence of the periplasmic ribose binding protein. RbsR is also homologous to a family of bacterial repressor proteins including LacI. This implies that the structure of the repressor consists of a two-domain binding protein portion attached to a DNA-binding domain having the four-helix structure of the LacI headpiece. The implications of these relationships to the mechanism of this class of repressors are discussed.