FIG. 2.

Transcription is impaired only downstream of the poly(A) site. (A) Cassettes are transcribed sequentially from the SV40 early promoter. Transcription of the mutant version of p377A174P〈C₉〉 was carried out as described in Materials and Methods except that 7 mM Mg²⁺ and 7 mM citrate were used, and transcription times were varied from 1 to 32 min. The top panel shows molar amounts of each cassette produced plotted on an arbitrary scale. The bottom panel shows molar ratios of each cassette produced relative to the 377-nt cassette. (B) Elongation efficiency drops after crossing the poly(A) site. The percent readthrough for each cassette on the wild-type template relative to that of the mutant is plotted, as for Fig. 1C, above a scale map of the template.