In vivo elongation rate analysis of thousands of genes simultaneously. (A) Averaged distribution of 4sUDRB-seq reads over the different biological repeats in all genes longer than 20 Kb in RNA harvested 4 or 8 min after DRB removal. To minimize distortion of the data by residual mature mRNA, only reads within introns were considered and averaged. (B, C). 4sUDRB-seq reads distribution along the RBBP6 and PFDN1 genes. Arrow marks the direction of transcription.