A genetic screen for terminator function in yeast identifies a role for a new functional domain in termination factor Nab3

• Type of Material: Article
• Authors: Travis J. Loya, Emory University; Thomas W. O'Rourke, Emory University; Daniel Reines, Emory University
• Language: English
• Date: 2012-05-07
• Publisher: Oxford University Press (OUP): Policy C - Option B
• Publication Version: Final Published Version
• Copyright Statement: © Loya et al. 2012 Published by Oxford University Press
• License: Creative Commons Attribution-Noncommercial 3.0 Unported
• Final Published Version (URL): http://nar.oxfordjournals.org/content/40/15/7476
• Title of Journal or Parent Work: Nucleic Acids Research
• ISSN: 0305-1048
• Volume: 40
• Issue: 15
• Start Page: 7476
• End Page: 7491
• Grant/Funding Information: Funding for open access charge: National Institutes of Health [GM46331 to D.R.].
• Research Categories: Chemistry, Biochemistry

Abstract

The yeast IMD2 gene encodes an enzyme involved in GTP synthesis. Its expression is controlled by guanine nucleotides through a set of alternate start sites and an intervening transcriptional terminator. In the off state, transcription results in a short non-coding RNA that starts upstream of the gene. Transcription terminates via the Nrd1-Nab3-Sen1 complex and is degraded by the nuclear exosome. Using a sensitive terminator read-through assay, we identified trans-acting Terminator Override (TOV) genes that operate this terminator. Four genes were identified: the RNA polymerase II phosphatase SSU72, the RNA polymerase II binding protein PCF11, the TRAMP subunit TRF4 and the hnRNP-like, NAB3. The TOV phenotype can be explained by the loss of function of these gene products as described in models in which termination and RNA degradation are coupled to the phosphorylation state of RNA polymerase II's repeat domain. The most interesting mutations were those found in NAB3, which led to the finding that the removal of merely three carboxy-terminal amino acids compromised Nab3's function. This region of previously unknown function is distant from the protein's well-known RNA binding and Nrd1 binding domains. Structural homology modeling suggests this Nab3 ‘tail’ forms an α-helical multimerization domain that helps assemble it onto an RNA substrate.