IDENTIFICATION OF A DECAY IN TRANSCRIPTION POTENTIAL THAT RESULTS IN ELONGATION-FACTOR DEPENDENCE OF RNA-POLYMERASE-II

The rate of RNA elongation by RNA polymerase II (pol II) is affected b y DNA sequences called intrinsic arrest sites. Efficient transcription through these sites requires elongation factor SII. In addition to th e sequence-specific features of the DNA, we show that the acquisition of SII-dependence is a function of its ''dwell-time'' at an arrest sit e. This temperature-dependent decay in elongation potential appears ir reversible, implying that factor-dependent and factor-independent elon gation complexes are not mutually interconvertible at this position. T FIIF and NH4Cl are known to increase the elongation rate of pol II. Bo th agents preempt arrest, consistent with the idea that elongation dwe ll time influences the process. TFIIF and SII act upon different steps in a complementary way to prevent or resolve arrest, respectively. Th ey are probably instrumental in facilitating the efficient transcripti on of large eukaryotic genes in vivo.