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J. Bacteriol., Mar 1997, 1541-1549, Vol 179, No. 5
J Horak and DH Wolf
When Saccharomyces cerevisiae cells growing on galactose are transferred
onto glucose medium containing cycloheximide, an inhibitor of protein
synthesis, a rapid reduction of Gal2p-mediated galactose uptake is
observed. We show that glucose-induced inactivation of Gal2p is due to its
degradation. Stabilization of Gal2p in pra1 mutant cells devoid of vacuolar
proteinase activity is observed. Subcellular fractionation and indirect
immunofluorescence showed that the Gal2 transporter accumulates in the
vacuole of the mutant cells, directly demonstrating that its degradation
requires vacuolar proteolysis. In contrast, Gal2p degradation is proteasome
independent since its half- life is unaffected in pre1-1 pre2-2, cim3-1,
and cim5-1 mutants defective in several subunits of the protease complex.
In addition, vacuolar delivery of Gal2p was shown to be blocked in
conditional end3 and end4 mutants at the nonpermissive temperature,
indicating that delivery of Gal2p to the vacuole occurs via the endocytic
pathway. Taken together, the results presented here demonstrate that
glucose- induced proteolysis of Gal2p is dependent on endocytosis and
vacuolar proteolysis and is independent of the functional proteasome.
Moreover, we show that Gal2p is ubiquitinated under conditions of
glucose-induced inactivation.
Copyright © 1997, American Society for Microbiology
Catabolite inactivation of the galactose transporter in the yeast Saccharomyces cerevisiae: ubiquitination, endocytosis, and degradation in the vacuole
Institute of Physiology, Department of Membrane Transport, Academy of Sciences of the Czech Republic, Prague.
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