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J. Bacteriol., Dec 1997, 7644-7652, Vol 179, No. 24
V Svetlov and TG Cooper
Regulated nitrogen catabolic gene transcription in Saccharomyces cerevisiae
is mediated by four positive (Gln3p and Gat1p/Nil1p) and negative
(Dal80p/Uga43p and Deh1p/Nil2p/GZF3p) regulators which function in
opposition to one another. All four proteins contain GATA- type zinc finger
domains, and three of them (Gln3p, Dal80p, and Deh1p) have been shown to
bind to GATA sequences situated upstream of genes whose expression is
sensitive to nitrogen catabolite repression (NCR). The positive regulators,
Gln3p and Gat1p, are able to support transcriptional activation when
tethered by LexAp to the promoter of a reporter gene whose upstream
activation sequences have been replaced with one or more lexA operator
sites. Existing data suggest that these four proteins regulate
transcription by competing with one another for binding to the GATA
sequences which mediate NCR-sensitive gene expression. We show that the
minimal Gln3p domain mediating transcriptional activation consists of 13
amino acids with a predicted propensity to form an alpha-helix. Genetic
analysis of this region (Gln3p residues 126 to 138, QQNGEIAQLWDFN)
demonstrated that alanine may be substituted for the aromatic and acidic
amino acids without destroying transcriptional activation potential.
Similar substitution of alanine for the two hydrophobic amino acids,
isoleucine and leucine, however, destroys activation, as does introduction
of basic amino acids in place of the acidic residues or introduction of
proline into the center of the sequence. A point mutation in the Gln3p
activation region destroys its in vivo ability to support NCR-sensitive
DAL5 expression. We find no convincing evidence that NCR regulates Gln3p
function by modulating the functioning of its activation region.
Copyright © 1997, American Society for Microbiology
The minimal transactivation region of Saccharomyces cerevisiae Gln3p is localized to 13 amino acids
Department of Microbiology and Immunology, University of Tennessee, Memphis 38163, USA.
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