Do DEAD-Box Proteins Promote Group II Intron Splicing without Unwinding RNA?

• DOI: 10.1016/j.molcel.2007.07.028
• Publication Date: 2007-11-26T18:25:27Z
• Authors: Mark Del Campo; Pilar Tijerina; Hari Bhaskaran; Sabine Mohr; Quansheng Yang; Eckhard Jankowsky; Rick Russell; Alan M. Lambowitz
• Keywords: DEAD box; Group II intron; RNA Helicase A; Exonic splicing enhancer; SR protein

The DEAD-box protein Mss116p promotes group II intron splicing in vivo and in vitro. Here we explore two hypotheses for how Mss116p promotes group II intron splicing: by using its RNA unwinding activity to act as an RNA chaperone or by stabilizing RNA folding intermediates. We show that an Mss116p mutant in helicase motif III (SAT/AAA), which was reported to stimulate splicing without unwinding RNA, retains ATP-dependent unwinding activity and promotes unfolding of a structured RNA. Its unwinding activity increases sharply with decreasing duplex length and correlates with group II intron splicing activity in quantitative assays. Additionally, we show that Mss116p can promote ATP-independent RNA unwinding, presumably via single-strand capture, also potentially contributing to DEAD-box protein RNA chaperone activity. Our findings favor the hypothesis that DEAD-box proteins function in group II intron splicing as in other processes by using their unwinding activity to act as RNA chaperones.