Structure of the cytosine–cytosine mismatch in the thymidylate synthase mRNA binding site and analysis of its interaction with the aminoglycoside paromomycin

(A) Isothermal titration calorimetry (ITC) profile of the paromomycin–TSMC interaction at pH 6.4, 10 mM sodium phosphate, 100 μM EDTA, recorded at 20°C. Two paromomycin molecules bind each TSMC RNA and a sequential two-site binding model was used to fit the data. (B) ITC profile of the titration of paromomycin into a RNA molecule where the CC mismatch in TSMC is replaced by a GC base pair. No binding is observed in B demonstrating the importance of the CC mismatch in paromomycin recognition.