Nucleotide excision repair affects the stability of long transcribed (CTG*CAG) tracts in an orientation-dependent manner in Escherichia coli

Many human hereditary neurological diseases, including fragile X syndrome, myotonic dystrophy, and Friedreich’s ataxia, are associated with expansions of the triplet repeat sequences (TRS) (CGG/CCG, CTG/CAG, and GAA/TTC) within or near specific genes. Mechanisms that mediate mutations of TRS include DNA replication, repair, and gene conversion and (or) recombination. The involvement of the repair systems in TRS instability was investigated in Escherichia coli on plasmid models, and the results showed that the deficiency of some nucleotide excision repair (NER) functions dramatically affects the stability of long CTG inserts. In such models in which there are tens or hundreds of plasmid molecules in each bacterial cell, repetitive sequences may interact between themselves and according to a recombination hypothesis, which may lead to expansions and deletions within such repeated tracts. Since one cannot control interaction between plasmids, it is also sometimes difficult to give precise interpretation of the results. Therefore, using modified lambda phage (λInCh), we have constructed a chromosomal model to study the instability of trinucleotide repeat sequences in E. coli. We have shown that the stability of (CTG/CAG)68 tracts in the bacterial chromosome is influenced by mutations in NER genes in E. coli. The absence of the uvrC or uvrD gene products greatly enhances the instability of the TRS in the chromosome, whereas the lack of the functional UvrA or UvrB proteins causes substantial stabilization of (CTG/CAG) tracts.

Download Full-text

Faculty Opinions recommendation of Involvement of the nucleotide excision repair protein UvrA in instability of CAG*CTG repeat sequences in Escherichia coli.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1000992.13404 ◽

2001 ◽

Author(s):

Richard Wood

Keyword(s):

Escherichia Coli ◽

Nucleotide Excision Repair ◽

Excision Repair ◽

Repeat Sequences ◽

Repair Protein ◽

Nucleotide Excision ◽

Nucleotide Excision Repair Protein ◽

Ctg Repeat

Download Full-text

Photolyases from Saccharomyces cerevisiae and Escherichia coli recognize common binding determinants in DNA containing pyrimidine dimers.

Molecular and Cellular Biology ◽

10.1128/mcb.9.11.4777 ◽

1989 ◽

Vol 9 (11) ◽

pp. 4777-4788 ◽

Cited By ~ 23

Author(s):

M Baer ◽

G B Sancar

Keyword(s):

Escherichia Coli ◽

Saccharomyces Cerevisiae ◽

Nucleotide Excision Repair ◽

Excision Repair ◽

Spectroscopic Studies ◽

Pyrimidine Dimer ◽

Nucleotide Sequence Analysis ◽

Binding Motif ◽

Pyrimidine Dimers ◽

Nucleotide Excision

DNA photolyases catalyze the light-dependent repair of pyrimidine dimers in DNA. The results of nucleotide sequence analysis and spectroscopic studies demonstrated that photolyases from Saccharomyces cerevisiae and Escherichia coli share 37% amino acid sequence homology and contain identical chromophores. Do the similarities between these two enzymes extend to their interactions with DNA containing pyrimidine dimers, or does the organization of DNA into nucleosomes in S. cerevisiae necessitate alternative or additional recognition determinants? To answer this question, we used chemical and enzymatic techniques to identify the contacts made on DNA by S. cerevisiae photolyase when it is bound to a pyrimidine dimer and compared these contacts with those made by E. coli photolyase and by a truncated derivative of the yeast enzyme when bound to the same substrate. We found evidence for a common set of interactions between the photolyases and specific phosphates in the backbones of both strands as well as for interactions with bases in both the major and minor grooves of dimer-containing DNA. Superimposed on this common pattern were significant differences in the contributions of specific contacts to the overall binding energy, in the interactions of the enzymes with groups on the complementary strand, and in the extent to which other DNA-binding proteins were excluded from the region around the dimer. These results provide strong evidence both for a conserved dimer-binding motif and for the evolution of new interactions that permit photolyases to also act as accessory proteins in nucleotide excision repair. The locations of the specific contacts made by the yeast enzyme indicate that the mechanism of nucleotide excision repair in this organism involves incision(s) at a distance from the pyrimidine dimer.

Download Full-text