FIGURE 5-12 Bacterial RNA polymerase. This structure corresponds to the polymerase molecule in the elongation stage (step 4) of Figure 5-11. In this diagram, transcription is proceeding in the rightward direction. Arrows indicate where downstream DNA enters the polymerase and upstream DNA exits at an angle from the downstream DNA. The template strand is light violet, the nontemplate strand, dark violet; the nascent RNA, red. The RNA polymerase β′ subunit is gold; the β subunit, light yellow; and the α subunits visible from this angle, brown. Nucleotides complementary to the template DNA are added to the 3′ end of the nascent RNA strand on the right side of the transcription bubble. The newly synthesized nascent RNA exits the polymerase at the upstream side through a channel formed by the β subunit. The ω subunit is also visible from this angle.

[Data courtesy of Seth Darst; see N. Korzheva et al., 2000, Science 289:619–625, and N. Opalka et al., 2003, Cell 114:335–345.]