Figure 4. The involvement of Tet(O) loops in Tc resistence.

(a) Alignment of C. jejuni Tet(O) (NCBI GI number 51209514), T. thermophilus EF-G (NCBI GI number 46199633) and consensus sequences of domain 4 from the Tet(O) and EF-G families. In the consensus sequences, a residue is capitalized if it present for more than 60% of the time in the full alignment; a lowercase letter shows 60% conservation within a common substitution group, and a dot shows a position that does not meet either of these thresholds. The secondary structure is indicated above the alignment with arrows for β strands, with the functionally important loops at the tip of the domain labeled. The sites of point mutations in Tet(O) are indicated by underlining, and three amino acid deletions by yellow highlighting. (b) Full-length Tet(O) homology model structure with domain 4 rendered in teal. Residues rendered in orange sticks are those subjected to mutational analysis, as shown in (a) and (c). (c) Tetracycline sensitivity measurements. The optical density at 600 nm after 12 h of bacterial growth at 37°C is plotted as a function of tetracycline concentration. Tetracycline concentration at which OD₆₀₀ was below 0.1 was treated as the MIC.