Candidate osmosensors from Candida utilis and Kluyveromyces lactis: structural and functional homology to the Sho1p putative osmosensor from Saccharomyces cerevisiae

In Saccharomyces cerevisiae, increases in external osmolarity evoke osmostr ess-induced signalling via the HOG MAP kinase pathway. One of the upstream components of this signal transduction route is the putative osmosensor, Sh o1p. With the aim to elucidate the molecular basis of osmosensing in buddin g yeast, we have cloned SHO1 homologues from Candida utilis and Kluyveromyc es lactis which allowed determination of conserved domains of Sho1p. Result s obtained from sequence comparisons, confirmed the importance of the trans membrane domains and the SH3 domain for Sho1p function. The K. lactis and S . cerevisiae Sho1p show the highest degree of homology, the isoform from C. utilis is a shorter protein. SHO1 from C. utilis, however, did complement the osmosensitivity of the sho1ssk2ssk22 strain by restoring HOG pathway fu nction, since Hog1p dual phosphorylation after high osmotic challenge was r estored in this strain after transformation with a plasmid bearing this SHO 1 homologue. (C) 2000 Elsevier Science B.V. All rights reserved.