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J Bacteriol, July 1998, p. 3533-3540, Vol. 180, No. 14
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Regulation of Expression of GLT1, the Gene Encoding Glutamate Synthase in Saccharomyces cerevisiae

Lourdes Valenzuela,1 Paola Ballario,2 Cristina Aranda,1 Patrizia Filetici,2 and Alicia González1,*

Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico,1 and Dipartimento di Genetica e Biologia Molecolare, Centro de Studio per gli Acidi Nucleici, Universitá "La Sapienza," 00185 Rome, Italy2

Received 12 March 1998/Accepted 12 May 1998

Saccharomyces cerevisiae glutamate synthase (GOGAT) is an oligomeric enzyme composed of three 199-kDa identical subunits encoded by GLT1. In this work, we analyzed GLT1 transcriptional regulation. GLT1-lacZ fusions were prepared and GLT1 expression was determined in a GDH1 wild-type strain and in a gdh1 mutant derivative grown in the presence of various nitrogen sources. Null mutants impaired in GCN4, GLN3, GAT1/NIL1, or UGA43/DAL80 were transformed with a GLT1-lacZ fusion to determine whether the above-mentioned transcriptional factors had a role in GLT1 expression. A collection of increasingly larger 5' deletion derivatives of the GLT1 promoter was constructed to identify DNA sequences that could be involved in GLT1 transcriptional regulation. The effect of the lack of GCN4, GLN3, or GAT1/NIL1 was also tested in the pertinent 5' deletion derivatives. Our results indicate that (i) GLT1 expression is negatively modulated by glutamate-mediated repression and positively regulated by Gln3p- and Gcn4p-dependent transcriptional activation; (ii) two cis-acting elements, a CGGN15CCG palindrome and an imperfect poly(dA-dT), are present and could play a role in GLT1 transcriptional activation; and (iii) GLT1 expression is moderately regulated by GCN4 under amino acid deprivation. Our results suggest that in a wild-type strain grown on ammonium, GOGAT constitutes an ancillary pathway for glutamate biosynthesis.

* Corresponding author. Mailing address: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-242, Mexico City 04510, Mexico. Phone: 6225631. Fax: 6225630. E-mail: amanjarr{at}ifisiol.unam.mx.

J Bacteriol, July 1998, p. 3533-3540, Vol. 180, No. 14
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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