Orientation of the erp, bppA, bppB, and bppC loci on B. burgdorferi cp32 (drawn to scale). erp loci may be either mono- or bicistronic. The start codon of bppC is located approximately 430 bp from the start codon of its adjacent erp locus. bppA encodes a 51-kDa protein, bppB encodes a 17-kDa protein, and bppC encodes a 32-kDa protein.