Syk ubiquitylation is reduced in Syk(Y317F) KI mice. (A) Representative western blots showing Syk pY346 in Syk(Y317F) (KI) and WT littermate control platelets stimulated various concentrations of CRP for 3 minutes at 37°C with stirring. (B) The ratios of the total intensity of high-molecular-weight species (pSyk-ubi) to the intensity of nonubiquitylated pSyk (pSyk no ubi) were quantified, analyzed, and presented as described in the “Materials and methods.” The ratio in nonstimulated platelets was not analyzed, as all intensities were close to 0. (C) Syk(Y317F) and WT littermate control platelets were stimulated with 1 μg/mL CRP for 60 seconds, the ubiquitylated proteins from their lysates were immunoprecipitated with the ubiquitin-trap reagent and immunoblotted for Syk, as described in the “Materials and methods.” A representative western blot of 2 experiments is presented.