Nuclear Gln3 Import Is Regulated by Nitrogen Catabolite Repression Whereas Export Is Specifically Regulated by Glutamine.
Gln3, a transcription activator mediating nitrogen-responsive gene expression in Saccharomyces cerevisiae, is sequestered in the cytoplasm, thereby minimizing nitrogen catabolite repression (NCR)-sensitive transcription when cells are grown in nitrogen-rich environments. In the face of adverse nitrogen supplies, Gln3 relocates to the nucleus and activates transcription of the NCR-sensitive regulon whose products transport and degrade a variety of poorly used nitrogen sources, thus expanding the cell's nitrogen-acquisition capability. Rapamycin also elicits nuclear Gln3 localization, implicating Target-of-rapamycin Complex 1 (TorC1) in nitrogen-responsive Gln3 regulation. However, we long ago established that TorC1 was not the sole regulatory system through which nitrogen-responsive regulation is achieved. Here we demonstrate two different ways in which intracellular Gln3 localization is regulated. Nuclear Gln3 entry is regulated by the cell's overall nitrogen supply, i.e., by NCR, as long accepted. However, once within the nucleus, Gln3 can follow one of two courses depending on the glutamine levels themselves or a metabolite directly related to glutamine. When glutamine levels are high, e.g., glutamine or ammonia as the sole nitrogen source or addition of glutamine analogues, Gln3 can exit from the nucleus without binding to DNA. In contrast, when glutamine levels are lowered, e.g., adding additional nitrogen sources to glutamine-grown cells or providing repressive nonglutamine nitrogen sources, Gln3 export does not occur in the absence of DNA binding. We also demonstrate that Gln3 residues 64-73 are required for nuclear Gln3 export.
Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163.
Rajendra
R
Rai
Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163.
Jennifer J
JJ
Tate
Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
Karthik
K
Shanmuganatham
Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163.
Martha M
MM
Howe
Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163.
David
D
Nelson
Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163 tcooper@uthsc.edu.
Terrance G
TG
Cooper
D021581:Active Transport, Cell Nucleus; D019943:Amino Acid Substitution; D001665:Binding Sites; D057465:Catabolite Repression; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
C071664:GLN3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D005973:Glutamine; D009584:Nitrogen
Gln3; glutamine; methionine sulfoximine; nitrogen catabolite repression; nuclear export; nuclear import; rapamycin