A Splicing-Dependent Transcriptional Checkpoint Associated with Prespliceosome Formation

There is good evidence for functional interactions between splicing and transcription in eukaryotes, but how and why these processes are coupled remain unknown. Prp5 protein (Prp5p) is an RNA-stimulated adenosine triphosphatase (ATPase) required for prespliceosome formation in yeast. We demonstrate through in vivo RNA labeling that, in addition to a splicing defect, the prp5-1 mutation causes a defect in the transcription of intron-containing genes. We present chromatin immunoprecipitation evidence for a transcriptional elongation defect in which RNA polymerase that is phosphorylated at Ser5 of the largest subunit’s heptad repeat accumulates over introns and that this defect requires Cus2 protein. A similar accumulation of polymerase was observed when prespliceosome formation was blocked by a mutation in U2 snRNA. These results indicate the existence of a transcriptional elongation checkpoint that is associated with prespliceosome formation during cotranscriptional spliceosome assembly. We propose a role for Cus2p as a potential checkpoint factor in transcription. [Display omitted] •Transcriptional elongation is inhibited when prespliceosome formation is blocked•The defect is characterized by RNA polymerase accumulation on introns•This checkpoint can be triggered by mutations in either PRP5 or U2 snRNA•The U2-associated Cus2 protein is a candidate checkpoint factor In eukaryotes, transcription and splicing are functionally linked, but how or why this happens is unknown. Chathoth et al. show that, in budding yeast, these processes are coupled by one or more transcriptional checkpoints associated with surveillance of the splicing machinery as it assembles cotranscriptionally on nascent transcripts.