The SNF1 kinase in Saccharomyces cerevisiae is an excellent
model to study the regulation and function of the AMP-dependent protein kinase
(AMPK) family of serine-threonine protein kinases. Yeast discoveries regarding
the regulation of this non-hormonal sensor of metabolic/environmental stress are
conserved in higher eukaryotes, including poly-ubiquitination of the α-subunit
of yeast (Snf1) and human (AMPKα) that ultimately effects subunit stability and
enzyme activity. The ubiquitin-cascade enzymes responsible for targeting Snf1
remain unknown, leading us to screen for those that impact SNF1 kinase function.
We identified the E2, Ubc1, as a regulator of SNF1 kinase function. The
decreased Snf1 abundance found upon deletion of Ubc1 is not due to increased
degradation, but instead is partly due to impaired SNF1 gene expression, arising
from diminished abundance of the Forkhead 1/2 proteins, previously shown to
contribute to SNF1 transcription. Ultimately, we report that
the Fkh1/2 cognate transcription factor, Hcm1, fails to enter the nucleus in the
absence of Ubc1. This implies that Ubc1 acts indirectly through transcriptional
effects to modulate SNF1 kinase activity.
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