Transcriptional regulators of the Schizosaccharomyces pombe fbp1 gene include two redundant Tup1p-like corepressors and the CCAAT binding factor activation complex
Rtk. Janoo et al., Transcriptional regulators of the Schizosaccharomyces pombe fbp1 gene include two redundant Tup1p-like corepressors and the CCAAT binding factor activation complex, GENETICS, 157(3), 2001, pp. 1205-1215
The Schizosaccharomyces pombe fbp1 gene, which encodes fructose-1,6-bis-pho
sphatase, is transcriptionally repressed by glucose through the activation
of the cAMP-dependent protein kinase A (PKA) and transcriptionally activate
d by glucose starvation through the activation of a mitogen-activated prote
in kinase (MAPK). To identify transcriptional regulators acting downstream
from or in parallel to PIU, we screened an adh-driven cDNA plasmid library
for genes that increase fbp1 transcription in a strain with elevated PKA ac
tivity. Two such clones express amino-terminally truncated forms of the S.
pombe tup12 protein that resembles the Saccharomyces cerevisiae Tup1p globa
l corepressor. These clones appear to act as dominant negative alleles. Del
etion of both tup12 and the closely related tup11 gene causes a 100-fold in
crease in fbp1-lacZ expression, indicating that tup11 and tup12 are redunda
nt negative regulators of fbp1 transcription. In strains lacking tup11 and
tup12 the atfl-pcrl transcriptional activator continues to play a central r
ole in fbp1-lacZ expression; however, spcl MAPK phosphorylation of atfl is
no longer essential for its activation. We discuss possible models for the
role of tup11- and tup12-mediated repression with respect to signaling from
the MAPK and PKA pathways. A third clone identified in our screen expresse
s the php5 protein subunit of the CCAAT-binding factor (CBF). Deletion of p
hp5 reduces fbp1 expression under both repressed and derepressed conditions
. The CBF appears to act in parallel to atfl-pcrl, although it is unclear w
hether or not CBF activity is regulated by PKA.