To determine the mechanisms that the yeast S. cerevisiae uses to adapt to osmotic stress, mutants were isolated which were impaired in their ability to accumulate glycerol in response to a high osmolarity challenge. These mutants identified four genes, HOG1 through HOG4 (High Osmolarity Glycerol Response). HOG2 was cloned from a genomic library on a centromere vector by complementation of the high osmolarity sensitive growth (Osm$\sp{\rm s}$) phenotype of hog2-1. Integrative confirmation of the genetic linkage between the cloned DNA and the locus of the original point mutation was performed. The null mutant hog2-$\Delta$3, created by deletion of the gene, had phenotypes similar to those of hog2-1. In addition to being Osm$\sp{\rm s}$, hog2-$\Delta$3 mutants are heat shock-sensitive, fail to accumulate glycogen and are defective for sporulation. We sequenced HOG2 and determined that this gene encodes a 102 kDa protein, the N-terminus of which contains a region of 350 amino acids showing 38% identity to CIF1(GLC6), a gene required for metabolic responses to glucose. HOG2 encodes trehalose-6-phosphate phosphatase. HOG2 mRNA levels increase in response to heat shock and osmotic stress. Yeast cells containing a HOG2::lacZ fusion showed a four-fold increase in $\beta$-galactosidase one hour after exposure to 0.5 M NaCl, but no increase was seen after a heat shock at 42$\sp\circ$ for one hour. The pleiotropic phenotype of hog2$\Delta$ mutants suggests that HOG2 is a regulatory gene necessary for adaptive responses to a variety of environmental stresses. We propose that the promoter region of HOG2 contains two separate stress elements in the Upstream Activating Sequence (UAS). We suggest that the HOG2 promoter region located between nucleotides $-$1 and $-$400 of the HOG2 coding region contains a novel osmotic stress element which is induced in response to an increased extracellular osmolarity. The inducement of this osmotic stress element is not dependent on the presence of the TRS, the heat shock inducible element, found farther upstream.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16760 |
| Date | January 1994 |
| Creators | Nye, Mary Ellen |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | application/pdf |
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