Using integrative structural biochemistry, project A4 will investigate the architecture of a large spliceosomal submodule, which consists of the Brr2 RNA helicase, the Snu114 G-protein and the Prp8 regulatory scaffold and which is required for RNP remodeling events that elicit spliceosome catalytic activation, as well as of its substrate complex. We will then analyze how molecular, submodular and modular functions of the spliceosome are affected by structure-guided site-directed mutagenesis and will also investigate how the submodule is regulated by reversible ubiquitination.