FIG. 6.

In vitro transcription with ς⁷⁰ mutants from KAB substrates. Reactions contained RNA polymerase core enzyme and the indicated GST-ς⁷⁰ fusion protein (0.5 pmol). The substrates contained either the extended −10 promoter (KAB-TG, left side) or a variant without the extended −10 element (KAB-TT, right side). The arrow indicates the runoff transcripts, roughly 900 bases in length. With the extended −10 substrate, GST-ς⁷⁰ Y571C produced about half as many transcripts as wild-type ς⁷⁰ and D570N produced about twice as many as wild type. Transcripts were not detected with any of the ς⁷⁰ proteins from the KAB-TT substrate. Size standards (in bases) are indicated to the left of the gel, and the round spots are film artifacts.