- In Saccharomyces cerevisiae the expression of the galactose/melibiose catabolic pathway genes is under the control of at least three regulatory genes, GAL4, GAL80, and GAL3. The mechanisms of the GAL80 and GAL3 proteins in the regulation of this response by the control of the transcription of the pathway genes were investigated. The GAL80 gene was cloned and a 1.5 kb transcript was identified. The pathway genes were constitutively expressed in the genetically engineered gal80-D null mutant at levels higher than a wild-type strain grown on galactose. The GAL80 protein was not required for induction and is one of the factors which limits transcription even in the induced state. Repression of transcription by glucose was observed in the wild-type strain and still occurred in the gal80-D mutant strain.
We determined that in a gal3 mutant strain the accumulation of GAL1-10-7 and MEL1 RNAs is delayed for 3 to 5 days. Either overexpression of the GAL4 protein or block imposed by a gal3 gal1 gal7 genotype. This suggests that GAL3 functions in induction at a step prior to GAL4 activation of transcription. A chromosomal disruption of the GAL3 gene results in a 3 to 5 day delay in induction. Loss of either the plasmid-borne GAL3 gene or the GAL1-10-7 genes results in a cessation of the induced state in gal3 gal1 gal7 cells even when galactose is present. Either GAL3 or GAL1-10-7 gene function are needed for induction and maintenance of the induced state. These pathways are independent.
We found three galactose inducible, glucose repressible, basally expressed GAL3 transcripts. All are regulated by GAL4 and GAL80 proteins. The transcripts are 2.1, 1.9, and 1.6 kb in size with abundance of 4, 1, and 13, respectively. Preliminary data suggests that 5' end differences may exist and will account for the dramatic 500 bp length difference.
Antisera to the GAL80 protein has been obtained by gene fusion technology.
Yeast strains that overproduce the GAL80 and GAL3 gene products have been created for future studies.
- Dissertation Note:
- Ph.D. The Pennsylvania State University 1986.
- Source: Dissertation Abstracts International, Volume: 47-04, Section: B, page: 1427.
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