Dynamic flexibility of DNA repair pathways in growth arrested Escherichia coli.

The DNA of all organisms is constantly damaged by exogenous and endogenous agents. Base excision repair (BER) is important for the removal of several non-bulky lesions from the DNA, however not much is known about the contributions of other DNA repair pathways to the processing of non-bulky lesions. Here we utilized a luciferase reporter system to assess the contributions of transcription-coupled repair (TCR), BER and nucleotide excision repair (NER) to the repair of two non-bulky lesions, 8-oxoguanine (8OG) and uracil (U), in vivo under non-growth conditions.

8-Oxoguanine-mediated transcriptional mutagenesis causes Ras activation in mammalian cells.

8-Oxoguanine (8OG) is efficiently bypassed by RNA polymerases in vitro and in bacterial cells in vivo, leading to mutant transcripts by directing incorporation of an incorrect nucleotide during transcription. Such transcriptional mutagenesis (TM) may produce a pool of mutant proteins. In contrast, transcription-coupled repair safeguards against DNA damage, contingent upon the ability of lesions to arrest elongating RNA polymerase.

Trypanosoma brucei has two distinct mitochondrial DNA polymerase beta enzymes.

In higher eukaryotes, DNA polymerase (pol) beta resides in the nucleus and participates primarily in DNA repair. The DNA polymerase beta from the trypanosomatid Crithidia fasciculata, however, was the first mitochondrial enzyme of this type described. Upon searching the nearly completed genome data base of the related parasite Trypanosoma brucei, we discovered genes for two pol beta-like proteins.

The mitochondrial DNA polymerase beta from Crithidia fasciculata has 5'-deoxyribose phosphate (dRP) lyase activity but is deficient in the release of dRP.

DNA polymerase beta (pol beta) has long been described as a nuclear enzyme involved in DNA repair. A pol beta from the trypanosomatid parasite Crithidia fasciculata, however, is the first example of a mitochondrial enzyme of this type. The mammalian nuclear enzyme functions not only as a nucleotidyl transferase but also has a dRP lyase activity that cleaves 5'-deoxyribose phosphate (dRP) groups from DNA, thus contributing to two consecutive steps of the base excision repair pathway.