The Prp19 and Msl5-Mud2 complexes coordinate transcription with nuclear mRNP assembly

Abstract

The process of gene expression is complex and involves multiple steps. In the first step, RNA polymerase II (RNAPII) synthesizes mRNA, which then undergoes co-transcriptional processing such as 5′-end capping, splicing, and polyadenylation. The processed mRNA is then packaged into a messenger ribonucleoprotein particle (mRNP), transported to the cytoplasm, and eventually translated into a protein. TREX is a key player of mRNP biogenesis by coupling transcription to nuclear mRNA export. Additionally, the Prp19 complex (Prp19C), well-known for its role in splicing, has been discovered to play an important role in gene expression by supporting transcription elongation by stabilizing TREX at transcribed genes. Prp19C contains eight core proteins; the essential subunits are Prp19, Cef1, Clf1, Syf1, Cwc2, and Prp46 and the non-essential subunits are Isy1, Ntc20, Syf2, and Snt309. However, it is unknown if the individual non-essential subunits of Prp19C play a role in maintaining TREX at transcribed genes and in transcription. In this study, I found out that Ntc20 does not have a role during transcription elongation. However, deletion of ISY1 leads to a loss of Prp19C and TREX occupancy’s at transcribed genes. Deletion of SNT309 elicits many effects, which in the end can be explained by a destabilization of the Prp19C. Cwc15 and Syf2 facilitate the interaction between TREX and Prp19C, as well as with the transcription machinery. Moreover, Cwc15 is essential for efficient transcription elongation. Msl5 is the branch point binding protein that plays a crucial role in splicing and interacts with Mud2. Recent research has shown that Mud2 is also involved in transcription elongation. Published PAR-CLIP data showed that Msl5 crosslinks to intronless mRNAs. However, its function in the biogenesis of intronless mRNAs remains unknown. Therefore, I wanted to investigate whether Msl5 has a role in transcription. In this work, I found out that Msl5 is needed for full occupancy of Prp19C and therefore TREX at transcribed genes. Further, if Msl5 is missing efficient export of mRNA is impaired at 37°C. In sum, this study is the first to determine specific functions for the non-essential subunits of Prp19C and further a novel function of Msl5 during transcription and nuclear mRNA export.