Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.7 (DNA polymerase)
 17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mitochondrial transcription machinery synthesizes the RNA primers required for initiation of leading-strand DNA synthesis in mammalian mitochondria. RNA primers are also required for initiation of lagging-strand DNA synthesis, but the responsible enzyme has so far remained elusive. Here, we present a series of observations that suggests that mitochondrial RNA polymerase (POLRMT) can act as lagging-strand primase in mammalian cells. POLRMT is highly processive on double-stranded DNA, but synthesizes RNA primers with a length of 25 to 75 nt on a single-stranded template. The short RNA primers synthesized by POLRMT are used by the mitochondrial DNA polymerase gamma to initiate DNA synthesis in vitro. Addition of mitochondrial single-stranded DNA binding protein (mtSSB) reduces overall levels of primer synthesis, but stimulates primer-dependent DNA synthesis. Furthermore, when combined, POLRMT, DNA polymerase gamma, the DNA helicase TWINKLE, and mtSSB are capable of simultaneous leading- and lagging-strand DNA synthesis in vitro. Based on our observations, we suggest that POLRMT is the lagging-strand primase in mammalian mitochondria.
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PMID:Human mitochondrial RNA polymerase primes lagging-strand DNA synthesis in vitro. 1868 3

In mammals, NRF-2 (nuclear respiratory factor 2), also named GA-binding protein, is an Ets family transcription factor that controls many genes involved in cell cycle progression and protein synthesis as well as in mitochondrial biogenesis. In this paper, we analyzed the role of NRF-2 in the regulation of human genes involved in mitochondrial DNA transcription and replication. By a combination of bioinformatic and biochemical approaches, we found that the factor binds in vitro and in vivo to the proximal promoter region of the genes coding for the transcription termination factor mTERF, the RNA polymerase POLRMT, the B subunit of the DNA polymerase-gamma, the DNA helicase TWINKLE, and the single-stranded DNA-binding protein mtSSB. The role of NRF-2 in modulating the expression of those genes was further established by RNA interference and overexpression strategies. On the contrary, we found that NRF-2 does not control the genes for the subunit A of DNA polymerase-gamma and for the transcription repressor MTERF3; we suggest that these genes are under regulatory mechanisms that do not involve NRF proteins. Since NRFs are known to positively control the expression of transcription-activating proteins, the novelty emerging from our data is that proteins playing antithetical roles in mitochondrial DNA transcription, namely activators and repressors, are under different regulatory pathways. Finally, we developed a more stringent consensus with respect to the general consensus of NRF-2/GA-binding protein when searching for NRF-2 binding sites in the promoter of mitochondrial proteins.
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PMID:Nuclear respiratory factor 2 induces the expression of many but not all human proteins acting in mitochondrial DNA transcription and replication. 1995 46

Mitochondrial DNA is replicated by a unique enzymatic machinery, which is distinct from the replication apparatus used for copying the nuclear genome. We examine here the mechanisms of origin-specific initiation of lagging-strand DNA synthesis in human mitochondria. We demonstrate that the mitochondrial RNA polymerase (POLRMT) is the primase required for initiation of DNA synthesis from the light-strand origin of DNA replication (OriL). Using only purified POLRMT and DNA replication factors, we can faithfully reconstitute OriL-dependent initiation in vitro. Leading-strand DNA synthesis is initiated from the heavy-strand origin of DNA replication and passes OriL. The single-stranded OriL is exposed and adopts a stem-loop structure. At this stage, POLRMT initiates primer synthesis from a poly-dT stretch in the single-stranded loop region. After about 25 nt, POLRMT is replaced by DNA polymerase gamma, and DNA synthesis commences. Our findings demonstrate that POLRMT can function as an origin-specific primase in mammalian mitochondria.
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PMID:Mitochondrial RNA polymerase is needed for activation of the origin of light-strand DNA replication. 2012 56

Ribonucleoside analogues have potential utility as anti-viral, -parasitic, -bacterial and -cancer agents. However, their clinical applications have been limited by off target effects. Development of antiviral ribonucleosides for treatment of hepatitis C virus (HCV) infection has been hampered by appearance of toxicity during clinical trials that evaded detection during preclinical studies. It is well established that the human mitochondrial DNA polymerase is an off target for deoxyribonucleoside reverse transcriptase inhibitors. Here we test the hypothesis that triphosphorylated metabolites of therapeutic ribonucleoside analogues are substrates for cellular RNA polymerases. We have used ribonucleoside analogues with activity against HCV as model compounds for therapeutic ribonucleosides. We have included ribonucleoside analogues containing 2'-C-methyl, 4'-methyl and 4'-azido substituents that are non-obligate chain terminators of the HCV RNA polymerase. We show that all of the anti-HCV ribonucleoside analogues are substrates for human mitochondrial RNA polymerase (POLRMT) and eukaryotic core RNA polymerase II (Pol II) in vitro. Unexpectedly, analogues containing 2'-C-methyl, 4'-methyl and 4'-azido substituents were inhibitors of POLRMT and Pol II. Importantly, the proofreading activity of TFIIS was capable of excising these analogues from Pol II transcripts. Evaluation of transcription in cells confirmed sensitivity of POLRMT to antiviral ribonucleosides, while Pol II remained predominantly refractory. We introduce a parameter termed the mitovir (mitochondrial dysfunction caused by antiviral ribonucleoside) score that can be readily obtained during preclinical studies that quantifies the mitochondrial toxicity potential of compounds. We suggest the possibility that patients exhibiting adverse effects during clinical trials may be more susceptible to damage by nucleoside analogs because of defects in mitochondrial or nuclear transcription. The paradigm reported here should facilitate development of ribonucleosides with a lower potential for toxicity.
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PMID:Sensitivity of mitochondrial transcription and resistance of RNA polymerase II dependent nuclear transcription to antiviral ribonucleosides. 2316 98