Fig. 1.

Dbr1 in pre-mRNA splicing and synthetic bRNAs used in this study. (A) The phosphate of the branching 2′,5′-phosphodiester bond is circled in red. The coloring of the branchpoint and flanking nucleotides is preserved throughout the manuscript. The sequence of the synthetic bRNAs AK86 is displayed, and the shorter AK49 sequence is boxed. (B) Cartoon representation of AK49, AK86, and AK88. (C) Dbr1-mediated hydrolysis of the fluorogenic bRNA AK88 permits the 2′- and 5′-arms to separate, relieving the quenching of the 5′-FAM fluorophore by the 2′-DABCYL moiety.