FIG. 3.

Amino acid sequences of the TP901-1 CI repressor protein. The gray boxes represent regions involved in DNA binding (helix-turn-helix motif) and oligomerization (residues 138 to 180) (23). The positions where five amino acids were inserted by transposon mutagenesis are shown above the sequences as triangles, and the numbers identify the positions of the inserts in CI. At two positions (78 and 89) marked with asterisks, five amino acids were inserted by site-specific mutagenesis. Three lines to the left of the sequence are marked with P_L, P_R, or P_Lmor, and the triangles in each line represent the state of P_L, P_R, or P_L in the presence of a functional mor gene, resulting from the given CI mutant, respectively. ▾, positions where linker insertion in CI abolish repression of P_L or P_R; ▿, positions where linker insertion still allows repression of P_L or P_R. Wild-type CI protein represses transcription from both P_L and P_R (white triangles) in the absence of mor. In the presence of a functional mor gene and wild-type CI, each transformant has a choice between two states, i.e., P_L repressed or P_L open (hatched triangle). Insertion of linkers at positions 98 and 135 showed wild-type phenotypes, but the repressed state of P_L was not inducible.