A new method for determining the number of RNA polymerases active in chromatin transcription

A new method is described for determining the number of RNA chains which are being actively propagated in an in vitro transcription system. This method employs [³²P]-α-cordycepin triphosphate which terminates RNA chain propagation upon incorporation of the nucleotide analogue into an RNA transcript. This method is quicker and subject to fewer problems than end group analysis using [³H]nucleoside triphosphates. The auxin-induced increase in soybean RNA polymerase I activity was examined using this method. At 12, 24, and 48 hours after auxin treatment, the increase in chromatin-bound RNA polymerase I activity is predominantly due to a greater rate of RNA chain elongation rather than to an increase in the number of elongating RNA chains.