FIGURE 2.

Effect of simple viscogens on transcript elongation by MRV cores. Results of representative experiments are shown. Transcripts were analyzed by 1% agarose gel electrophoresis. Transcripts elongated for 1 min are estimated to be ∼600 nt, whereas those elongated for only 10–15 s, as in control samples, are estimated to be only 100–150 nt. A, cores were allowed to transcribe for 10 s (upper) or 15 s (lower) in regular transcription buffer including [α-³²P]CTP. The reaction was then stopped, and after changing the medium, samples were allowed to elongate with nonradiolabeled NTPs for 40 s (upper) or 45 s (lower) in the presence of indicated concentrations of glycerol (upper) or sucrose (lower). An aliquot of preinitiated transcripts prior to continued elongation (no elong.) was also analyzed for each experiment. B, cores were allowed to transcribe for 15 s in regular transcription buffer including [α-³²P]CTP. The reaction was then stopped, and after changing the reaction medium, samples were allowed to elongate with nonradiolabeled NTPs for 50 s; for this step, UTP concentration was either 1 mm (lane 2) or 0.03 mm (lane 3). An aliquot of preinitiated transcripts prior to continued elongation was also analyzed (lane 1). C, cores were allowed to transcribe for 15 s in regular transcription buffer including [α-³²P]CTP. The reaction was then stopped, and after changing the medium, samples were allowed to elongate with nonradiolabeled NTPs including 0.03 mm UTP for 110 s in the presence of indicated concentrations of glycerol.