Figure 3. Effect of camptothecin reversal on RNA synthesis.

(A), Aggregate view of RNA synthesis of genes larger than 100 kb in normal human fibroblasts with the genes aligned by transcriptional start sites (TSS). RNA synthesis recovers as a wave in a 5’-to-3’ direction following camptothecin removal with no apparent recovery of RNA polymerases stalled in the body of the genes. Elongation rates of the recovering transcription wave was estimated to be ~1.2 kb/min. (B), Wave of recovery of RNA synthesis can be seen advancing from the 5’-end of the CD44 gene with no apparent recovery in the body of the gene. The front of the transcription wave extended some 35 kb during the first 30 min recovery resulting in an elongation rate of about 1.2 kb/min. (C) Similar elongation rates after camptothecin removal were found for the MEISE1 gene. Color key: Blue, control (30 min Bru labeling); Yellow, Bru labeling during the last 15 min of a 45 min camptothecin treatment; Green, 45 min camptothecin treatment followed by a drug washout and 15 min of Bru labeling; Red, 45 min camptothecin treatment followed by a drug washout, 15 min incubation, and finally 15 min Bru labeling.