a, Summary of the pipeline used for the identification of intron functions. b, Validation of the BSP PCR assay to detect variation in cell number. Intron-deletion cells were diluted with wild-type cells and the BSP PCR was performed on each dilution; the amplicon amount was plotted as function of dilution. The mean value of two independent experiments is presented and the s.d. is indicated by error bars. The correlation value (Spearman correlation coefficient) is indicated. This figure is related to Fig. 1.