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Mol. Cell. Biol., Oct 1996, 5876-5887, Vol 16, No. 10
WC Smart, JA Coffman and TG Cooper
CAR1 (arginase) gene expression responds to multiple environmental signals;
expression is induced in response to the intracellular accumulation of
arginine and repressed when readily transported and catabolized nitrogen
sources are available in the environment. Up to 14 cis-acting sites and 9
trans-acting factors have been implicated in regulated CAR1 transcription.
In all but one case, the sites are redundant. To test whether these sites
actually participate in CAR1 expression, each class of sites was
inactivated by substitution mutations that retained the native spacing of
the CAR1 cis-acting elements. Three types of sites function independently
of the nitrogen source: two clusters of Abflp- and Rap1p-binding sites, and
a GC-rich sequence. Two different sets of nitrogen source-dependent sites
are also required: the first consists of two GATAA-containing UASNTR sites
that mediate nitrogen catabolite repression-sensitive transcription, and
the second is arginine dependent and consists of three UAS1 elements that
activate transcription only when arginine is present. A single URS1 site
mediates repression of CAR1 arginine-independent upstream activator site
(UAS) activity in the absence of arginine and the presence of a poor
nitrogen source (a condition under which the inducer-independent Gln3p can
function in association with the UASNTR sites). When arginine is present,
the combined activity of the UAS elements overcomes the negative effects
mediated by URS1. Mutation of the classes of sites either singly or in
combination markedly alters CAR1 promoter operation and control, supporting
the idea that they function synergistically to regulate expression of the
gene.
Copyright © 1996, American Society for Microbiology
Combinatorial regulation of the Saccharomyces cerevisiae CAR1 (arginase) promoter in response to multiple environmental signals
Department of Microbiology and Immunology, University of Tennessee, Memphis 38163, USA.
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