Competition between pre-mRNAs for a limiting splicing machinery drives global changes in splicing

During meiosis in yeast, global splicing efficiency increases. The mechanism for this is relief of competition for the splicing machinery by repression of intron-containing ribosomal protein genes (RPGs). Repression of RPGs with rapamycin also increases splicing efficiency in vegetative cells. Reducing levels of an RPG-dedicated transcription factor globally improves splicing and suppresses the temperature-sensitive growth defect of a spliceosome mutation. These results indicate that the spliceosome is limiting and pre-mRNAs compete with each other. Under these conditions, splicing efficiency of a given pre-mRNA therefore depends on both its concentration and affinity for the limiting splicing factor(s) as well as those of the competing pre-mRNAs. We propose that trans-competition control of splicing helps repress meiotic gene expression in vegetative cells, and promotes efficient meiosis. Competition between RNAs for a limiting factor may be a general condition important for function of a variety of post-transcriptional control mechanisms. Splicing and gene expression profiles of 1) wild type yeast cells treated with rapamycin (2 biological replicates) relative to untreated cells and 2) prp4-1 pGAL-IFH1 (down-regulated expression of IFH1 transcription factor(specific for ribosomal protein genes)) relative to prp4-1 yeast.