Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

7,8-Dihydro-8-oxoguanine (8-oxoG) is the most frequent mutagenic lesion caused by oxidative stress. Eukaryotic cells use a specific DNA glycosylase, OGG1, to excise 8-oxoG from DNA. The mild phenotype of OGG1 null mice has been attributed to the existence of alternative pathways, including Cockayne syndrome B (CSB)-dependent transcription coupled repair (TCR), for removal of 8-oxoG. We have studied repair and transcription activities at 8-oxoG lesions with a reconstituted transcription system (RTS; RNA polymerase II, TBP, TFIIA, TFIIB, TFIIE, TFIIF and TFIIH), as well as in cellular extracts and in vivo. All measurable repair activity at 8-oxoG lesions takes place in the 3'-direction from the lesion, indicating base excision repair (BER) activity and negligible role of nucleotide excision repair (NER). Although 8-oxoG has been shown to be preferentially removed from the transcribed strand, in vitro experiments with purified transcription factors failed to identify a definite block for RNA polymerase II at the lesion. However, a weak block was observed at the lesion during transcription carried out with RTS as well as with cellular extracts. RNA polymerase II was identified at the site of the lesion on obstructed templates. Wild-type cells, as well as cells carrying targeted mutations of genes required for removal of 8-oxoG, were transfected with a luciferase expression vector containing an 8-oxoG lesion. No significant obstruction at 8-oxoG lesions was observed by this in vivo approach. In control experiments transcription elongation was completely blocked by cisplatin.
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PMID:Transcription activities at 8-oxoG lesions in DNA. 1538 Jan 1

RpoS is a bacterial sigma factor of RNA polymerase which is involved in the expression of a large number of genes to facilitate survival under starvation conditions and other stresses. The results of our study demonstrate that the frequency of emergence of base substitution mutants is significantly increased in long-term-starved populations of rpoS-deficient Pseudomonas putida cells. The increasing effect of the lack of RpoS on the mutation frequency became apparent in both a plasmid-based test system measuring Phe(+) reversion and a chromosomal rpoB system detecting rifampin-resistant mutants. The elevated mutation frequency coincided with the death of about 95% of the cells in a population of rpoS-deficient P. putida. Artificial overexpression of superoxide dismutase or catalase in the rpoS-deficient strain restored the survival of cells and resulted in a decline in the mutation frequency. This indicated that, compared to wild-type bacteria, rpoS-deficient cells are less protected against damage caused by reactive oxygen species. 7,8-Dihydro-8-oxoguanine (GO) is known to be one of the most stable and frequent base modifications caused by oxygen radical attack on DNA. However, the spectrum of base substitution mutations characterized in rpoS-deficient P. putida was different from that in bacteria lacking the GO repair system: it was broader and more similar to that identified in the wild-type strain. Interestingly, the formation of large deletions was also accompanied by a lack of RpoS. Thus, the accumulation of DNA damage other than GO elevates the frequency of mutation in these bacteria. It is known that oxidative damage of proteins and membrane components, but not that of DNA, is a major reason for the death of cells. Since the increased mutation frequency was associated with a decline in the viability of bacteria, we suppose that the elevation of the mutation frequency in the surviving population of carbon-starved rpoS-deficient P. putida may be caused both by oxidative damage of DNA and enzymes involved in DNA replication and repair fidelity.
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PMID:Elevated mutation frequency in surviving populations of carbon-starved rpoS-deficient Pseudomonas putida is caused by reduced expression of superoxide dismutase and catalase. 1934 6