Fig. 7

Van Holde - Weischet integral G(s) sedimentation coefficient distributions for CASKIN2 at 10 μM (wild type, blue; G537D/K540E double mutant, cyan) and 34 μM (wild type, green; G537D/K540E double mutant, red) loading concentrations. Panels a and b were measured at 150 mM NaCl, while panels c and d were measured at 300 mM NaCl. A shift in sedimentation coefficient for higher concentrations indicates reversible mass action. This effect is only seen for the wild type, not for the double mutant. Furthermore, the effect is enhanced at higher ionic strength, indicative of a decrease in K _d for the wild type. These results indicate that the double mutant only exists in a monomeric form at low concentration, while the wild type SAM tandem dimerizes and is more sensitive to changes in ionic strength