Initiation of RNA Synthesis in Isolated Nuclei (original) (raw)

Ribonucleotide triphosphates, labeled at the 8 position, were synthesized and used directly to quantify RNA chain initiation in nuclei isolated from Friend cells grown in tissue culture. At the optimal salt concentration, low-molecular-weight RNAs (4 -5 S) synthesized by RNA polymerase I11 were the predominant species initiated. Less than 5 of the molecules were initiated by polymerase 11. We calculate that 50 -80 % of the small RNA molecules synthesized in vitro were also initiated in vitro. Assuming that a substantial fraction of the nuclei were active in vitro, the number of 4-5 S RNA molecules initiated per nucleus was about 100 molecules/min.