In this project, we investigated how the spliceosome bound to an excised intron-lariat is remodeled and how the associated intron-lariat is debranched during the process collectively known as spliceosome termination. We used a native pulldown from a C. elegans strain carrying an endogenous tag on the spliceosome subunit PRP19 to identify factors involved in terminal splicing events. We tagged these proteins (DHX35, YJU2B, and DBR1) ectopically in human K562 cells to define the composition of terminal spliceosome intermediates by native pulldowns. We also analyzed the interactomes of several termination factors (YJU2B, DBR1, and CWF19L1), including that of the putative spliceosome quality control factor LENG1, by biotin proximity labeling in human HEK293T cells. Finally, we investigated how the terminal spliceosome bound to a debranched intron and DHX35 is remodeled. Together, our data reveal the composition and remodeling steps of terminating human spliceosomes.