ACT1-CUP1 Assays Determine the Substrate-specific Sensitivities of Spliceosomal Mutants in Budding Yeast

Mutations introduced in the spliceosome or its substrate have significantly contributed to our understanding of the intricacies of spliceosomal function. Whether disease-related or functionally selected, many of these mutations have been studied using growth assays in the model organism Saccharomyces cerevisiae (yeast). The splicing-specific copper growth assay, or ACT1-CUP1 assay, provides a comprehensive analysis of mutation at the phenotypic level. The ACT1-CUP1 assay utilizes reporters that confer copper tolerance when correctly spliced. Thus, in the presence of copper, changes in yeast viability correlate to changes in mRNA production through splicing. In a typical experiment, the yeast spliceosome is challenged with different non-consensus splicing reporters and the splicing factor mutation of interest to detect any synergetic or antithetical impact on splicing. Here a full description of copper plate preparation, plating of yeast cells, and data evaluation are given. A selection of complimentary experiments is described, highlighting the versatility of the ACT1-CUP1 reporters. The ACT1-CUP1 assay is a handy tool in the splicing toolbox thanks to the direct read-out of mutational effect(s) and the comparative possibilities from the continuing use in the field.