title: RasG regulates discoidin gene expression during Dictyostelium growth.
abstract: Activated rasG, rasG(G12T), was expressed in Dictyostelium cells under the control of the folate-repressible discoidin promoter (pVEII-rasG(G12T)) and found to have a unique pattern of expression when cells were transferred to folate-deficient media: an initial increase of RasG(G12T) resulting from the removal of folate, followed by a rapid decline while cells were still in the early exponential phase of growth. Discoidin levels were considerably lower and declined more rapidly in the pVEII-rasG(G12T) transformant than they did in the wild type, suggesting that RasG(G12T) represses discoidin expression. This was independently confirmed by placing the rasG(G12T) gene under the control of the ribonucleotide reductase (rnrB) promoter. Exposure of cells to 10 mM methyl methanesulfonate (MMS) rapidly generated RasG(G12T) and this was accompanied by an equally rapid decrease in discoidin mRNA levels. rasG null cells also contained decreased levels of discoidin under all conditions tested, indicating that RasG is essential for optimum discoidin expression. However, rasG null cells showed normal regulation of discoidin expression in response to PSF, CMF, folate, bacteria, and axenic media, indicating that RasG is not necessary for any of these responses. These results reveal a role for RasG in regulating discoidin gene expression and add a further level of complexity to the regulation of the discoidin promoter.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, 6174 University Boulevard, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: D M
authors.initials: DM
authors.lastname: Secko
authors.forename: M
authors.initials: M
authors.lastname: Khosla
authors.forename: P
authors.initials: P
authors.lastname: Gaudet
authors.forename: A
authors.initials: A
authors.lastname: Tsang
authors.forename: G B
authors.initials: GB
authors.lastname: Spiegelman
authors.forename: G
authors.initials: G
authors.lastname: Weeks
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics*; D002478:Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D000070821:Discoidins; D005492:Folic Acid / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology*; D037102:Lectins; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics*; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000070821:Discoidins; D037102:Lectins; D015800:Protozoan Proteins; C424065:rasG protein, Dictyostelium; D005492:Folic Acid