title: Nutrient-induced activation of trehalase in nutrient-starved cells of the yeast Saccharomyces cerevisiae: cAMP is not involved as second messenger.
abstract: Starvation of Saccharomyces cerevisiae cells for specific nutrients such as nitrogen, phosphate or sulphate causes arrest in the G1 phase of the cell cycle at a specific point called 'start'. Re-addition of different nitrogen sources, phosphate or sulphate to such starved cells causes activation of trehalase within a few minutes. Nitrogen-source- and sulphate-induced activation of trehalase were not associated with any change in the cAMP level, but in the case of phosphate there was a small transient increase. When nitrogen-source-activated trehalase was isolated by immuno-affinity chromatography from crude extracts, the purified enzyme showed the same activity profile as in the original crude extracts, indicating that post-translational modification is responsible for the activation. In the yeast mutants cdc25-5 and cdc35-10, which are temperature sensitive for cAMP synthesis, incubation at the restrictive temperature lowered but did not prevent nitrogen-, phosphate- or sulphate-induced activation of trehalase. Since under these conditions the cAMP level in the cells is very low, it is unlikely that cAMP acts as a second messenger in this nutrient-induced effect. Nitrogen-source-induced activation of trehalase requires the presence of glucose at a concentration similar to that able to stimulate the RAS-adenylate cyclase pathway. This indicates that the same glucose-sensing system might be involved in both phenomena. Nitrogen-starved cells fractionated according to cell size all showed nitrogen-source-induced activation of trehalase to the same extent, indicating that the nitrogen-induced signalling pathway involved is not dependent on the well-known cell size requirement for progression over the start point of the cell cycle.
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit te Leuven, Flanders, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Hirimburegama
authors.forename: P
authors.initials: P
authors.lastname: Durnez
authors.forename: J
authors.initials: J
authors.lastname: Keleman
authors.forename: E
authors.initials: E
authors.lastname: Oris
authors.forename: R
authors.initials: R
authors.lastname: Vergauwen
authors.forename: H
authors.initials: H
authors.lastname: Mergelsberg
authors.forename: J M
authors.initials: JM
authors.lastname: Thevelein
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D003470:Culture Media / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation; D015966:Gene Expression Regulation, Fungal; D011905:Genes, ras; D005947:Glucose / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism*; D015290:Second Messenger Systems; D014198:Trehalase / Q000378:metabolism*
chemical_list: D003470:Culture Media; D010710:Phosphates; D000643:Ammonium Chloride; D000242:Cyclic AMP; D014198:Trehalase; D005947:Glucose