a, Increasing the number of genes that contain nutrient-independent introns does not affect growth. Growth profile of wild-type cells transformed with empty plasmids or a plasmid expressing the TUB1 gene (which contains an intron that has no effect on cell growth under starvation conditions). The experiments were repeated independently four times with similar results. b–d, Genes that contain nutrient-independent introns do not rescue the intron-deletion phenotype. Growth profile of mms2∆i, ysf3∆i or glc7∆i cells transformed with plasmid expressing the intron-containing TUB1 gene. For b–d, the growth assays were repeated independently six times with similar results. e, f, Intron deletions are genetically epistatic. The growth profiles of wild-type (black), single (red) and double (blue) ∆i strains were monitored for 48 h in minimal medium that is low in dextrose. The experiments were repeated independently eight times with similar results. The position of the log phase and stationary phase of the growth are indicated on the growth curves. This figure is related to Figs. 3, 4.