Northwest University 1 article published in JoVE Genetics ACT1-CUP1 Assays Determine the Substrate-Specific Sensitivities of Spliceosomal Mutants in Budding Yeast Clarisse van der Feltz1 1College of Arts and Sciences, Northwest University The ACT1-CUP1 assay, a copper growth assay, provides a quick readout of precursor messenger RNA (pre-mRNA) splicing and the impact mutant splicing factors have on spliceosomal function. This study provides a protocol and highlights the customization possible to address the splicing question of interest.