FIGURE 4.
Binding of Crc to RNA fragments including the leader regions of the mRNAs originating at the Pu, Pm, PS1, and PR1 promoters. The ability of Crc (106, 212, 425, 850, or 1,700 nm) to bind to the indicated radioactively labeled RNA fragments was determined by band-shift assays in the presence of 1 μg of tRNA. The free RNA and the retarded band corresponding to the Crc-RNA complex are indicated as F and C, respectively. The presumed Crc target on each RNA is indicated in boldface. The AUG start codons of xylU (Pu and PuΔ15 RNAs), xylX (Pm RNA), xylS (PS1 RNA), and xylR (PR1 RNA) are boxed. The putative Shine-Dalgarno sequences are underlined. The transcription initiation sites corresponding to the PS2 and PR2 promoters are indicated by circled letters.