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Requirement for ERCC-1 and ERCC-3 gene products in DNA excision repair in vitro. Complementation using rodent and
1Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Herts, United Kingdom.
Abstract:
Numerous rodent cell lines exist that have defects in nucleotide excision repair of DNA caused by alterations in genes that fall into 10 different complementation groups. The precise roles in the repair of these genes are unknown. We report here that extracts from Chinese hamster ovary cells of excision repair-defective complementation groups 1 and 3 are defective in DNA excision repair in a cell-free system. In vitro complementation can be achieved by mixing extracts from the two groups with one another. In addition, extracts from a human cell line representing xeroderma pigmentosum complementation group B could complement rodent complementation group 1 extracts, but not group 3 extracts. This is consistent with an identity of the ERCC-3 and xeroderma pigmentosum group B genes. Cellular evidence points toward a defect in the incision of damaged DNA in group 1 and 3 mutants. Since the ERCC-1 and ERCC-3 proteins are required for the in vitro reaction, it appears that both gene products are directly involved in the enzymatic incision of damaged DNA, or in preincision reactions. The experiments reported here provide the biochemical basis of an approach to analyze the function of these nucleotide excision repair proteins.
Insights
Researchers identified key proteins involved in DNA repair. Mixing cell extracts from different DNA repair defects (complementation groups 1 and 3) restored DNA excision repair, revealing crucial roles for ERCC-1 and ERCC-3 proteins in this process.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Rodent cell lines with DNA nucleotide excision repair defects are classified into 10 complementation groups.
- The specific functions of genes within these complementation groups remain largely unknown.
Purpose of the Study:
- To investigate the roles of genes in DNA excision repair using cell-free systems.
- To biochemically characterize DNA repair defects in specific complementation groups.
Main Methods:
- Utilized cell-free extracts from Chinese hamster ovary (CHO) cell lines with excision repair defects (complementation groups 1 and 3).
- Performed in vitro complementation assays by mixing different cell extracts.
- Tested complementation between rodent and human (xeroderma pigmentosum group B) cell line extracts.
Main Results:
- Extracts from complementation groups 1 and 3 were defective in cell-free DNA excision repair.
- Mixing extracts from groups 1 and 3 restored DNA repair activity.
- Human xeroderma pigmentosum group B extract complemented group 1 but not group 3 rodent extracts.
- Evidence suggests a defect in DNA incision in group 1 and 3 mutants.
Conclusions:
- ERCC-1 and ERCC-3 proteins are essential for the in vitro DNA excision repair reaction.
- These proteins likely play direct roles in the enzymatic incision of damaged DNA or preincision steps.
- The findings provide a biochemical foundation for studying nucleotide excision repair protein functions.