Figure 4.

Transcript elongation is rapid. (A) The schematic depicts the method used to measure the rate at which a short RNA transcript elongates into a full-length RNA. The promoter template contained a mutation in which the A/T base pair at +1 was mutated to G/C (12). As diagrammed, the limited nucleotide substrates CpG, CTP, UTP, and ctDNA allowed the synthesis of a 16-nt transcript. When given ATP the 16-nt RNA elongates into the full-length 86-nt RNA. (B) Elongation of the 16-nt RNA to a full-length RNA occurs within 30 s. Nucleotides were at final concentrations of 1 mM CpG/625 μM UTP/25 μM [α-³²P]CTP (5 μCi per reaction). Elongation occurred after the addition of 625 μM ATP. The RNA products were resolved by 8% denaturing PAGE, and different exposures were used to show the full-length and 16-nt RNAs.