From Structure to Systems: High-Resolution, Quantitative Genetic Analysis of RNA Polymerase II

• Functional dissection of RNAPII by genetic interaction profiling of point mutants
• RNAPII mutations affect transcription initiation, splicing, and chromosome segregation
• Genetic relationships with RNAPII mutations reveal key transcription factors
• Start site selection and splicing efficiency are coordinated with transcription rate

SummaryRNA polymerase II (RNAPII) lies at the core of dynamic control of gene expression. Using 53 RNAPII point mutants, we generated a point mutant epistatic miniarray profile (pE-MAP) comprising ∼60,000 quantitative genetic interactions in Saccharomyces cerevisiae. This analysis enabled functional assignment of RNAPII subdomains and uncovered connections between individual regions and other protein complexes. Using splicing microarrays and mutants that alter elongation rates in vitro, we found an inverse relationship between RNAPII speed and in vivo splicing efficiency. Furthermore, the pE-MAP classified fast and slow mutants that favor upstream and downstream start site selection, respectively. The striking coordination of polymerization rate with transcription initiation and splicing suggests that transcription rate is tuned to regulate multiple gene expression steps. The pE-MAP approach provides a powerful strategy to understand other multifunctional machines at amino acid resolution.

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