Pra1, a novel
protein in S. cerevisiae, that regulates GCN4 levels independent of
GCN2.
Brian Luke (1),
Matthias Gstaiger (2), Wilhelm Krek (2), Matthias Peter (1)
(1) Biochemistry, ETH-Zürich, Hönggerberg, Zürich, 8093, Switzerland
(brian.luke@bc.biol.ethz.ch); (2) Friedrich Miescher Institute, Maulbeerstrasse
66, 4058 Basel, Switzerland
When nutrients
are limiting uncharged tRNAs accumulate, which bind to and activate the kinase,
GCN2.
In turn, activated GCN2 phosphorylates the alpha subunit of the eif2 translation
initiation factor, thereby down-regulating translation initiation. This pathway
is conserved throughout eukaryotes, and disregulation of this pathway may have
implications in metabolic diseases. In the budding yeast Saccharomyces
cerevisiae,
although activation of this pathway leads to general inhibition of translation
initiation, it causes the increased translation of a single transcript coding
for the transcription factor, GCN4. We have identified a novel protein, Pra1, that
when deleted causes the increased expression of GCN4, and constitutive
phosphorylation of eif2a, even in non-starvation conditions. Through microarray
analysis we have found that in a pra1-Δ, 85% of the derepressed genes have a GCN4
consensus sequence in their promoter. pra1Δ cells are temperature sensitive and this
Ts phenotype is rescued by further deletion of GCN4. In contrast, the
deletion of GCN2
does not rescues the Ts phenotype nor does it lead to reduced expression of GCN4 in a pra1Δ background,
although it completely abolished phosphorylation of eif2a. Interestingly, Pra1p
is downregulated during starvation and entry into stationary phase. Our results
indicate that Pra1p is a regulator of the nutrient response pathway, which,
when depleted leads to up-regulation of GCN4 in a GCN2 independent manner.