Figure 1.

(A) The N-terminal headpiece of LacI in complex with its operator (PDB: 1L1M). The backbone of the headpiece is shown in red. The side chains of Tyr17 and Gln18 are shown as yellow sticks. Base pairs in direct contacts with the repressor in the DNA major groove are shown in green and the rest of the DNA are shown in gray. This graph has been generated using PyMol. (B) The nucleotide sequences of the five operator variants considered in this work. Conserved nucleotides are shown in bold. (C) Amino acid sequences around the DNA recognition helix in LacI wild type (R1) and mutants (R2–R5). Residues 17 and 18 in R1 and the mutated residues in R2–R5 are shown in bold. (D) A graphical representation of the repression matrix associated with R1–R5 and Olac1–Olac5. The values represent the repression ratios, defined as the promoter activity at the presence of the input LacI variant over that in absence of the input LacI, measured for promoters each containing a single-operator element at the position +10. The yellow boundary encloses the subgroup associated with a diagonal repression matrix, suggesting within-subgroup pairwise specificity.