Statistical analysis of MS data is described in the previous section. For experiments with effects measured as fold changes relative to a control within each experiment, fold changes were log2 transformed and statistical significance was determined on the basis of a one-sample t test asking if the mean (of minimum three independent experiments) was different from 0 (Fig. 5, B to E, and fig. S7B). Significance testing for data in fig. S5 (D and E) was performed by a two-sample t test with a Sidak-Bonferroni correction for multiple testing. A statistically significant difference was concluded when P < 0.05.