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Identification of Streptococcus pneumoniae mismatch repair genes by an additive transformation approach
Abstract:
During transformation of Streptococcus pneumoniae, mismatch repair occurs on donor-recipient heteroduplexes harboring some mismatched base pairs. A few mutants defective in mismatch repair have been isolated and termed hex-. However, neither the number of genes involved nor their products have yet been identified. In an attempt to characterize such genes we have used an additive transformation approach--that is the inactivation of genes by insertion of chimeric plasmids. Pneumococcal DNA fragments were joined in vitro to a plasmid derivative of pBR325 that carries an erythromycin resistance determinant and does not replicate autonomously in S. pneumoniae. Ery-r transformants obtained with such a ligation mixture arise via homology-dependent integration of the chimeric plasmids into the chromosome. Hex- mutants have been selected among the ery-r population. Comparison of these mutants by Southern blot hybridization with a vector probe reveals that at least two genes are involved in mismatch repair.
Insights
Streptococcus pneumoniae uses mismatch repair during transformation. Researchers identified at least two genes involved in this process by creating and analyzing mutants defective in mismatch repair.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Mismatch repair is crucial for genetic transformation in Streptococcus pneumoniae, correcting errors in DNA heteroduplexes.
- Previous studies identified mutants defective in mismatch repair, termed hex- mutants, but the specific genes and their products remained unknown.
Purpose of the Study:
- To characterize the genes involved in mismatch repair in Streptococcus pneumoniae.
- To identify the number of genes contributing to the hex- phenotype.
Main Methods:
- Utilized an additive transformation approach involving gene inactivation by insertion of chimeric plasmids.
- Constructed chimeric plasmids by ligating pneumococcal DNA fragments to a non-replicating plasmid derivative (pBR325 with erythromycin resistance).
- Selected erythromycin-resistant (Ery-r) transformants, which arose from homology-dependent plasmid integration, and screened for hex- mutants.
Main Results:
- Successfully isolated hex- mutants using the described transformation method.
- Southern blot hybridization analysis of the isolated mutants revealed the involvement of at least two distinct genes in mismatch repair.
- Demonstrated the utility of chimeric plasmid insertion for gene characterization in Streptococcus pneumoniae.
Conclusions:
- At least two genes are essential for mismatch repair in Streptococcus pneumoniae.
- The study provides a foundation for further identification and characterization of the specific genes and proteins involved in pneumococcal mismatch repair.
- The employed methodology is effective for genetic dissection of essential cellular processes in Streptococcus pneumoniae.