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Yeast mutator phenotype enforced by Arabidopsis PMS1 expression
Celina Galles1, Claudia P Spampinato
1Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000, Rosario, Argentina.
Abstract:
The DNA mismatch repair (MMR) system is a major DNA repair pathway whose function is critical for the correction of DNA biosynthetic errors. MMR is initiated by the binding of MutS proteins to mismatches and unpaired nucleotides followed by the recruitment of MutL proteins. The major MutL activity in eukaryotes is performed by MutLα, the heterocomplex of MLH1-PMS1 in yeast and plants and MLH1-PMS2 in humans. We here report the effect the expression of Arabidopsis PMS1 protein exerts on Saccharomyces cerevisiae genomic stability. A strain carrying specific microsatellite instability reporter systems was chosen for the study. The plant protein failed to complement the hypermutator phenotype of a pms1 deficient strain but increased approximately 14-fold and 2,000-fold the mutation rates of his7-2 and lys2::InsE-A 14 loci of MMR proficient strains when compared to wild-type strains, respectively. Overexpressing AtMLH1 in the AtPMS1-overproducing strain generated an increase in mutation rate comparable to that of AtPMS1 expression alone. Deletion of the C-terminal residues implicated in protein-protein interaction and including the putative endonuclease sequence of AtPMS1 completely eliminated the mutator phenotype. Taken together, these results indicate that the plant proteins affect yeast genomic stability, very possibly altering protein-protein interactions that are necessary to complete repair.
Insights
The plant protein Arabidopsis PMS1 disrupts DNA mismatch repair (MMR) in yeast, increasing mutation rates. This suggests plant proteins can interfere with crucial DNA repair interactions in other species.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The DNA mismatch repair (MMR) system corrects errors during DNA replication, crucial for genomic stability.
- In eukaryotes, MutLα (MLH1-PMS1 in yeast/plants, MLH1-PMS2 in humans) is key for MMR.
- Understanding inter-species protein interactions in MMR is vital for evolutionary and functional insights.
Purpose of the Study:
- To investigate the impact of Arabidopsis thaliana PMS1 (AtPMS1) expression on Saccharomyces cerevisiae genomic stability.
- To determine if AtPMS1 can functionally complement yeast pms1 deficiency or affect MMR-proficient yeast.
Main Methods:
- Utilized yeast strains with specific microsatellite instability reporter systems.
- Assessed mutation rates in MMR-proficient and MMR-deficient yeast strains expressing AtPMS1.
- Examined the effect of AtMLH1 co-expression and AtPMS1 C-terminal deletions on mutation rates.
Main Results:
- AtPMS1 did not complement the hypermutator phenotype in pms1-deficient yeast.
- AtPMS1 significantly increased mutation rates (14-fold and 2,000-fold) in MMR-proficient yeast strains at specific loci.
- Overexpressing AtMLH1 with AtPMS1 yielded similar mutation rate increases; C-terminal deletions of AtPMS1 abolished this effect.
Conclusions:
- Arabidopsis PMS1 expression disrupts Saccharomyces cerevisiae genomic stability.
- The plant protein likely interferes with essential protein-protein interactions within the yeast MMR pathway.
- Specific domains of AtPMS1, particularly those involved in protein interactions and endonuclease activity, are critical for this mutator phenotype.
