The elongation of transcripts by RNA polymerase II is a complex process dependent upon nucleotide substrate levels, elongation factors, and co-transcriptional events such as splicing. Mutations in genes encoding elongation factor SI I (TFIIS), other elongation factors, RNA polymerase subunits, and chromatin related proteins, render S. cerevisiae sensitive to the drugs 6-azauracil and mycophenolic acid. These drugs are inhibitors of IMP dehydrogenase (IMPDH) which is a critical enzyme in the de novo pathway of guanine nucleotide synthesis. Its abundance is positively correlated with cell growth in eukaryotes from yeast to humans. Drug treated yeast respond by transcriptional induction of one of their four IMPDH genes. The response is reliant upon an optimally functioning elongation machinery. In humans, T lymphocyte proliferation during an immune response is highly dependent upon IMPDH synthesis. Mycophenolic acid inhibits T cell proliferation and is an important clinical immunosuppressant that inhibits graft rejection in kidney transplant (and other) patients. Mutations in IMPDH have also been implicated in the etiology of retinitis pigmentosa. Regulation of the essential yeast IMPDH gene family is mediated through a cellular mechanism that senses nucleotide pools. This project will use biochemistry and genetics to understand this regulation of IMPDH transcription through novel DNA elements. One sequence is a potent repressive element which encompasses the transcription start site and may regulate elongation. Yeast contain a complex family of IMPDH isoforms with varying sensitivity to mycophenolic acid inhibition. The potential of IMPDH to form heteromeric complexes between drug resistant and sensitive subunits will be addressed. The drug sensitive phenotype of yeast lacking their IMPDH genes will be useful in studying resistant and sensitive forms in humans. Resistance to IMPDH-directed drugs is an important clinical issue given the wide spread and lifelong treatment of transplant patients with mycophenolate. The ability of normal T cells, and T cells from patients receiving therapy, to respond to the drug by altering IMPDH expression and activity, will be examined. Differences between the responses of different individuals will be quantified. This will be important for the long term goal of understanding potential genetic differences in the efficacy of therapy and responsiveness of patients to immunosuppressants that target IMPDH.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics B Study Section (MGB)
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Tompkins, Laurie
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Emory University
Schools of Medicine
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O'Rourke, Thomas W; Reines, Daniel (2016) Determinants of Amyloid Formation for the Yeast Termination Factor Nab3. PLoS One 11:e0150865
Loya, Travis J; Reines, Daniel (2016) Recent advances in understanding transcription termination by RNA polymerase II. F1000Res 5:
O'Rourke, Thomas W; Loya, Travis J; Head, PamelaSara E et al. (2015) Amyloid-like assembly of the low complexity domain of yeast Nab3. Prion 9:34-47
Arndt, Karen M; Reines, Daniel (2015) Termination of Transcription of Short Noncoding RNAs by RNA Polymerase II. Annu Rev Biochem 84:381-404
Loya, Travis J; O'Rourke, Thomas W; Degtyareva, Natalya et al. (2013) A network of interdependent molecular interactions describes a higher order Nrd1-Nab3 complex involved in yeast transcription termination. J Biol Chem 288:34158-67
Loya, Travis J; O'Rourke, Thomas W; Reines, Daniel (2013) Yeast Nab3 protein contains a self-assembly domain found in human heterogeneous nuclear ribonucleoprotein-C (hnRNP-C) that is necessary for transcription termination. J Biol Chem 288:2111-7
Loya, Travis J; O'Rourke, Thomas W; Reines, Daniel (2012) A genetic screen for terminator function in yeast identifies a role for a new functional domain in termination factor Nab3. Nucleic Acids Res 40:7476-91
Reines, Daniel (2012) Decapping goes nuclear. Mol Cell 46:241-2
Jenks, M Harley; O'Rourke, Thomas W; Reines, Daniel (2008) Properties of an intergenic terminator and start site switch that regulate IMD2 transcription in yeast. Mol Cell Biol 28:3883-93
Kopcewicz, Katarzyna A; O'Rourke, Thomas W; Reines, Daniel (2007) Metabolic regulation of IMD2 transcription and an unusual DNA element that generates short transcripts. Mol Cell Biol 27:2821-9

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