Opening the Doors for Nuclear Gln3 Entry In Saccharomyces cerevisiae

Abstract

The Gln3 and Gat1 GATA transcription activators are responsible for Nitrogen Catabolite Repression‐sensitive transcription in the yeast Saccharomyces cerevisiae. In the presence of excess, usable nitrogen, Gln3 is cytoplasmic and NCR‐sensitive transcription repressed. When cells are grown in nitrogen‐poor medium, treated with the TorC1 inhibitor, rapamycin, or glutamine synthetase inhibitor, methionine sulfoximine (Msx), Gln3 becomes highly nuclear and NCR‐sensitive transcription derepressed. In previous reports, nuclear Gln3 localization was concluded to be mediated by a single nuclear localization sequence, NLS1. Here we show that nuclear Gln3‐Myc13 localization is more complex than previously appreciated. We have identified three Gln3 sequences, other than NLS1 that are almost absolutely required for nuclear Gln3‐Myc13 localization. Two of these sequences exhibit characteristics of monopartite (K/R‐Rich NLS) and bipartite (S/R NLS) NLSs, respectively. Mutations altering these sequences are partially epistatic to a ure2Δ. In contrast, a third sequence, the Ure2 Relief Sequence (URS), exhibits no predicted NLS homology and is only necessary when Ure2 is present. Substitution of the basic amino acid repeats in the Ure2 relief sequence or phosphomimetic aspartate substitutions for the serine residues between those basic residues abolish nuclear Gln3‐Myc13 localization in response to both limiting nitrogen and rapamycin treatment. In contrast, Gln3 responses are normal in parallel serine to alanine substitution mutants. These observations suggest that Gln3 responses to specific nitrogen environments likely occur in multiple, genetically separable steps. At least one general step, i.e., that associated with the Ure2 relief sequence, appears to be prerequisite for Gln3 responses to specific stimuli, e.g., growth in poor nitrogen sources and rapamycin inhibition of TorC1.Support or Funding InformationNational Institutes of Health General Medical Sciences GM‐35642‐27This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.