Transcription termination promotes splicing efficiency and fidelity in a compact genome

Splicing of terminal introns is coupled to 3′-end processing by cleavage and polyadenylation (CPA) of mRNAs in mammalian genes. Whether this functional coupling is universally conserved across eukaryotes is unknown. Here we show using long read RNA sequencing in S . cerevisiae that splicing inactivation does not result in widespread CPA impairment and that inactivation of CPA does not lead to global splicing defects. However, 5′-extensions due to termination defects from upstream genes lead to splicing inhibition in a length-dependent manner. Additionally, for some extended RNAs resulting from failed termination, we observed decreased splicing fidelity resulting in novel intergenic and long-range intragenic splicing events. These results argue against a broad coupling of splicing to CPA in S . cerevisiae but show that efficient CPA-mediated transcription termination is critical for splicing fidelity and efficiency in a compact genome.