CYT-19 destabilizes tertiary docking of the P1 helix into the <i>Tetrahymena</i> ribozyme core.

<p>(A) Cartoon of the ribozyme showing P1 helix docking, undocking, and unwinding rate constants in the presence of CYT-19, with the corresponding rate constants without CYT-19 in parentheses (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s008" target="_blank">Table S1</a>). (B) Representative FRET traces and histograms showing reversible docking (transitions shown in red) without CYT-19 (top), with CYT-19 and ATP (middle traces), and with CYT-19 and AMP–PNP (bottom). (C and D) Lifetime distributions of the docked (C) and undocked (D) states without CYT-19 (black) or with 0.5 µM (blue) or 1 µM (green) CYT-19 and 2 mM ATP-Mg²⁺ (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s002" target="_blank">Figures S2</a>, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s008" target="_blank">Tables S1</a>, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s009" target="_blank">S2</a>, and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s013" target="_blank">Data S1</a>, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s014" target="_blank">S2</a>). (E) Lifetime distributions of undocked P1 in the presence of 2 µM CYT-19 with AMP–PNP (red, left plot), without nucleotide (pink, center plot), and with ADP (orange, right plot). In each plot, corresponding data in the absence of CYT-19 and for 2 µM CYT-19 with ATP are shown for comparison in black and blue, respectively (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s008" target="_blank">Table S1</a> and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001981#pbio.1001981.s013" target="_blank">Data S1</a>).