Molecular weight of PCAF HAT domain determined by MALS. A) A running profile of PCAF protein at concentration of 20 mg/ml. PCAF HAT domain was first run on a gel filtration column detected by light scattering (LS11, shown in red) and refractive index (dRI, shown in blue). The X axis is a running time taken from the HPLC. The LS11 (one of 18 light scattering detectors) and dRI intensities are aligned and scaled. A relative scale is shown as the Y axis. Peak 1 is small and thus highlighted by an arrow. B) The molecular weight of the PCAF HAT domain at different concentrations. The measurements are colored in green (2 mg/ml), blue (6 mg/ml) and red (20 mg/ml). The dotted lines represent averaged values for molecular weight calculated by 18 laser detectors at each time point. The X axis is the same HPLC running time as (A) and the Y axis indicates molecular weight. C) The molecular weights of two PCAF particles in solution. The number in parenthesis is an error rate, which was calculated using the measurements of all time points for each peak in panel B. ND is ‘Not able to Determine’ because of low signal.