Related Experiment Videos
Extragenic suppressors of mar2(sir3) mutations in Saccharomyces cerevisiae
Abstract:
The silent mating-type genes (HML and HMR) of Saccharomyces cerevisiae are kept under negative transcriptional control by four trans-acting MAR (or SIR) loci. We have isolated extragenic suppressors of the mar2-1 mutation which, based on genetic complementation tests, define two additional loci involved in regulating the expression of HML and HMR. A strain with the genotype HMLa MAT alpha HMRa mar2-1 is sterile due to the simultaneous expression of a and alpha information. Two mutants exhibiting an alpha phenotype (which may result from the restoration of MAR/SIR repression) were isolated and genetically characterized. The mutations in these strains: (1) are recessive, (2) are capable of suppressing a mar2-deletion mutation, (3) are unlinked to MAT, (4) complement one another as well as the previously identified sum1-1 mutation, and (5) are not new alleles of the known MAR/SIR loci. We designate these new regulatory loci SUM2 and SUM3 (suppressor of mar). Unlike the sum1-1 mutation, suppression by sum2-1 and sum3-1 is mar2-locus specific. Both sum2-1 and sum3-1 affect the expression of a information at the HM loci. Transcript analysis shows a significant reduction in HMLa and HMRa gene transcription in mar2-1 sum2-1 and mar2-1 sum3-1 cells. Furthermore, we have found genetic evidence to suggest that mar2-1 sum2-1 cells exhibit only partial expression of silent alpha information. We conclude that the SUM2 and SUM3 gene products are required for expression of the HM loci and act downstream of the MAR2 (SIR3) gene function. Possible mechanisms for the action of the SUM gene products are discussed.
Insights
New genes SUM2 and SUM3 regulate silent mating-type genes (HML and HMR) in yeast. These genes are crucial for expressing mating information and act downstream of the MAR2 (SIR3) gene, impacting yeast fertility.
Area of Science:
- Molecular Biology
- Yeast Genetics
- Gene Regulation
Background:
- Silent mating-type genes HML and HMR in Saccharomyces cerevisiae are regulated by MAR/SIR loci.
- Transcriptional control ensures proper cell identity and mating.
- Dysregulation leads to sterility due to simultaneous expression of a and alpha information.
Purpose of the Study:
- To identify novel genetic factors involved in the regulation of HML and HMR.
- To characterize the function of newly discovered suppressor loci, SUM2 and SUM3.
- To elucidate the relationship between MAR/SIR loci and the SUM genes.
Main Methods:
- Isolation and genetic characterization of extragenic suppressors of the mar2-1 mutation.
- Complementation tests to identify new loci.
- Phenotypic analysis (mating assays) and transcript analysis (Northern blotting).
- Genetic mapping to determine linkage to MAT and other MAR/SIR loci.
Main Results:
- Two new regulatory loci, SUM2 and SUM3, were identified.
- Mutations sum2-1 and sum3-1 are recessive, unlinked to MAT, and complement sum1-1.
- Suppression by sum2-1 and sum3-1 is specific to the mar2 locus and affects HMLa and HMRa expression.
- SUM2 and SUM3 gene products are required for HM locus expression and act downstream of MAR2 (SIR3).
Conclusions:
- SUM2 and SUM3 are essential for the expression of silent mating-type information at HML and HMR.
- The SUM2 and SUM3 gene products function downstream of the MAR2 (SIR3) gene.
- These findings provide new insights into the complex regulatory network controlling yeast mating-type gene expression.