FIG. 5.

Effects of UTP concentration on transcription from the carAB P1 promoter. Standard in vitro transcription reactions in which the UTP concentration was varied as indicated were performed. End-labeled transcripts were separated on a 25% polyacrylamide sequencing gel, visualized by autoradiography, and quantitated. (A) Autoradiograph of the gel. Full-length transcripts (bracket) and nucleotide lengths of transcripts produced by simple abortive initiation are indicated on the left. Nucleotide lengths of GUUUU_n transcripts produced by reiterative transcription are shown on the right. (B) The levels of the full-length, GU₉, and GU₃GC₂AG transcripts plotted as a function of UTP concentration. The units for transcript levels are arbitrary.