PROTEIN-KINASE SCK1 IS INVOLVED IN TREHALASE ACTIVATION BY GLUCOSE AND NITROGEN-SOURCE IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

Trehalase activity is markedly enhanced upon addition of glucose and a nitrogen source to cells of the fission yeast Schizosaccharomyces pom be. This increase corresponds to a post-translational activation of th e enzyme, which is controlled by cAMP-dependent and cAMP-independent p athways. Recent work has shown that overexpression of SCK1 in Schiz. p ombe is able to suppress mutations that result in reduced Pka1 (cAMP-d ependent protein kinase A activity, suggesting that Sck1 (suppressor o f loss of AMP-dependent protein kinase) might be a functional analogue of Pka1 in the fission yeast. Here, an analysis of the possible role of Sck1 in the activation of trehalase triggered by glucose and a nitr ogen source is reported in cells that were deficient in either Pka1, S ck1 or both protein kinases. The results showed that, except in repres sed cells, Sck1 probably mediates a cAMP-independent activation of tre halase following the signal(s) triggered by glucose and the nitrogen s ource. The absence of functional Sck1 in derepressed cells renders tre halase insensitive to activation by glucose and the nitrogen source ev en in the presence of Pka1, indicating that the Sck1-dependent, cAMP-i ndependent pathway is the main signalling pathway controlling trehalas e activation under derepression conditions. It is proposed that, durin g the activation of trehalase induced by glucose or a nitrogen source, the cAMP-Pka1 activation pathway previously characterized is to some extent parallel to this newly described one which includes Sck1 as pho sphorylating enzyme. Neither of these two pathways, however, plays a k ey role in the heat-induced increase in trehalase activity.