New Suppressors of THO Mutations Identify Thp3 (Ypr045c)-Csn12 as a Protein Complex Involved in Transcription Elongation

Abstract

Formation of a ribonucleoprotein particle (mRNP) competent for export requires the coupling of transcription with mRNA processing and RNA export. A key link between these processes is provided by the THO complex. To progress in our understanding of this coupling, we have performed a search for suppressors of the transcription defect caused by the hpr1Δ mutation. This has permitted us to identify mutations in the genes for the RNA polymerase II mediator component Med10, the Sch9 protein kinase, and the Ypr045c protein. We report a role in transcription elongation for Ypr045c (Thp3) and the Csn12 component of the COP9 signalosome. Thp3 and Csn12 form a complex that is recruited to transcribed genes. Their mutations suppress the gene expression defects of THO complex mutants involved in mRNP biogenesis and export and show defects in mRNA accumulation. Transcription elongation impairment of thp3Δ mutants is shown by in vivo transcript run-on analysis performed in G-less systems. Thp3-Csn12 establishes a novel link between transcription and mRNA processing that opens new perspectives on our understanding of gene expression and reveals novel functions for a component of the COP9 signalosome. Thp3-Csn12 also copurifies with ribosomal proteins, which opens the possibility that it has other functions in addition to transcription.

ACKNOWLEDGMENTS

We thank D. Brow for plasmids, R. Luna and A. Rondón for critical reading of the manuscript, S. Juarez and S. Ciordia from the Proteomic Unit of CNB for the MALDI-TOF identification of the Thp3 proteome, and D. Haun for style supervision.

This work was supported by grants from the Spanish Ministry of Science and Education (BFU2006-05260 and BFU2007-28647-E) and Junta de Andalucía (BIO102 and CVI2549). S.J. was the recipient of a Juan de la Cierva grant from the Spanish Ministry of Science and Innovation. M.R. was funded by Koningin Wilhelmina Fonds and Stichting Nijmegen Universiteits Fonds.

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.01188-10.