U2 snRNA accessibility is regulated by NTP hydrolysis. (A) Secondary structure of the U2 snRNA with the BSL (bottom) or unwound interaction with the gray intron (top). The position of complementary DNA oligonucleotides used for RNase H digestion are indicated with colored bars. (B) Primer extension analysis of U2 snRNA isolated from nuclear extract after RNase H digestion. Extracts were treated with ATP, GTP, or AMP–PNP, or no NTP. Control digestions were carried out with a noncomplementary DNA oligonucleotide. (C) Cleavage efficiency was determined as band intensity in the region complementary to the oligonucleotide over the intensity of the entire lane of three independent trials. Statistical differences relative to the NTP sample were examined by unpaired Student's t-test.
