Fig. 2.

The toxT 5′ UTR fourU RNA thermometer facilitates temperature-dependent access to the SD sequence. Enzymatic cleavage of 5′ ³²P-end-labeled toxT RNA was carried out at 20 °C, 30 °C, and 37 °C. RNA fragments were separated on 15% polyacrylamide. (A) RNase T1 (cuts 3′ of single-stranded guanines) was used at the indicated concentrations [0.01 U (+) and 0.1 U (++)]. (B) RNase V1 (cuts double-stranded, stacked regions) was used at 0.1 U. Lane L is the alkaline ladder, lane N contains no RNase, and RNA was cleaved with 0.1 U T1 at 42 °C in lane T. WT indicates the native toxT 5′ UTR, and U5, 7C indicates the U5C U7C toxT 5′ UTR. The SD sequence is labeled, and select nucleotides are noted.