A splicing-dependent transcriptional checkpoint associated with pre-spliceosome 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 is an RNA-stimulated ATPase required for pre-spliceosome formation in yeast. We demonstrate through in vivo RNA labelling 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 serine 5 of the largest subunit’s heptad repeat accumulates over introns, and that this defect requires the U2 snRNP-associated Cus2p. A similar accumulation of polymerase was observed when pre-spliceosome formation was blocked by a mutation in U2 snRNA. These results indicate the existence of a transcriptional elongation checkpoint that is associated with pre-spliceosome formation during co-transcriptional spliceosome assembly. We propose a role for Cus2p as a potential checkpoint factor in transcription. Examining the Pol II profile in MT strain and WT strain