“The spliceosome is a complex molecular machine, composed of small nuclear ribonucleoproteins (snRNPs) and accessory proteins, that excises introns from precursor messenger RNAs (pre-mRNAs).  After assembly, the spliceosome is activated for catalysis by rearrangement of subunits to form an active site.” This study used multi-wavelength single-molecule fluorescence (“CoSMoS”) techniques to elucidate the mechanism of budding yeast spliceosome activation.  Activation turns out to be unexpectedly dynamic and variable: some spliceosomes  take multiple attempts to activate and the pathway contains both reversible and irreversible steps.  Strikingly, ATP powers both steps that drive the process forward toward splicing and well as reverse steps that diassemble intermediates to allow subsequent re-attempts at activation. These findings give new insight into how the efficiency and fidelity of pre-mRNA splicing is maintained.

The scientific project in this paper was initiated by Aaron Hoskins during his postdoctoral work in Melissa Moore’s and Jeff Gelles’ labs, but it was brought to fruition by Aaron and Margaret Rodgers working in Aaron’s lab at Univ. Wisconsin, Madison.