Fig. 4. The kinetics of serum induction and subsequent transcription of the beta-actin gene. (A to F) Images captured the progression of transcription into the 3'-UTR from quiescence at 0 min (A), one site active at 3 min (B), both sites at 5 min (C), peak of transcriptional activity and RNA export at 10 min (D) and 15 min (E), to a decline at 60 min (F). (G) Quantitative analysis of the transcription sites. The histogram indicates the mean number of nascent RNA on the gene (green) in the cell population at various times after induction and the mean number of nascent RNA that entered the 3'-UTR (red). The error bars indicate variation in transcriptional activity between the beta-actin alleles in the same cell as well as within the cell population. The signal from the 5' and 3' end of one mature mRNA is represented as a scale (c). (H) Separate regression curves were fitted to the following intervals: (section a) 0 to 5 min, before termination; (section b) 5 to 15 min, transcripts were terminating while the total number of transcripts on the gene continued to increase, and the number of RNAs in the 3'-UTR reached a plateau; (section c) 15 to 30 min, a slow decline in the total number of nascent RNA with little change in the number located in the 3'-UTR; and (section d) 30 to 120 min, an exponential decline in the total number of nascent RNA and in RNA reaching the 3'-UTR. (I) A dynamic profile of transcription at one beta-actin allele resolved with three spectrally distinct probes (14). The 5'-UTR probe detects all the nascent RNA (green). A second probe detects RNA that has progressed beyond the first 50 bases of the 3'-UTR (red), and the third probe detects RNA that has progressed to the distal region of the 3'-UTR (blue). The triple A's indicate transcripts beyond the polyadenylation site. Bar = 5 µm.