Dominant effects of tubulin overexpression in Saccharomyces cerevisiae.
The consequences of altering the levels of alpha- and beta-tubulin in Saccharomyces cerevisiae were examined by constructing fusions of the structural genes encoding the tubulins to strong galactose-inducible promoters. Overexpression of beta-tubulin (TUB2) was lethal: cells arrested in the G2 stage of the cell cycle exhibited an increased frequency of chromosome loss, were devoid of microtubules, and accumulated beta-tubulin in a novel structure. Overexpression of the major alpha-tubulin gene (TUB1) was not lethal and did not affect chromosome segregation. The rate of alpha-tubulin mRNA and protein synthesis was increased, but the protein did not accumulate. Overexpression of both alpha- and beta-tubulin together resulted in arrested cell division, and cells accumulated excess tubules that contained both alpha- and beta-tubulin. Transient overexpression of both tubulins resulted in a high frequency of chromosome loss. These data suggest that strong selective pressure exists to prevent excess accumulation of microtubules or beta-tubulin and suggest a model by which this goal may be achieved by selective degradation of unassembled alpha-tubulin. Furthermore, the phenotype of beta-tubulin overexpression is similar to the phenotype of a beta-tubulin deficiency. These results add to a number of recent studies demonstrating that mutant phenotypes generated by overexpression can be informative about the function of the gene product.
Burke
D
D
Department of Genetics, University of Washington, Seattle 98195.
Gasdaska
P
P
Hartwell
L
L
D002453:Cell Cycle; D002875:Chromosomes; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D005800:Genes, Fungal; D005804:Genes, Lethal; D008870:Microtubules / Q000648:ultrastructure; D009154:Mutation; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D014404:Tubulin / Q000096:biosynthesis / Q000235:genetics*
D014404:Tubulin