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RNase mitochondrial RNA processing correctly cleaves a novel R loop at the mitochondrial DNA leading-strand origin of
1Department of Developmental Biology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, California 94305-5427, USA.
Abstract:
The precursor primer RNA for mammalian mitochondrial DNA leading-strand replication remains as a persistent R loop formed during transcription through the mitochondrial DNA control region. We have examined model R loops, which exist in a novel and physiologically accurate preprimer conformation, as potential substrates for mammalian RNase mitochondrial RNA processing (MRP). Mouse RNase MRP accurately cleaves an R loop containing the mouse mitochondrial DNA origin. The multiple cleavage sites on the R-loop substrate match the priming sites observed in vivo, suggesting that RNase MRP alone is capable of generating virtually all of the leading-strand replication primers.
Insights
Mitochondrial RNA processing (MRP) enzyme accurately cleaves R-loops, generating essential primers for mammalian mitochondrial DNA replication. This suggests RNase MRP alone initiates most leading-strand DNA synthesis.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Mammalian mitochondrial DNA (mtDNA) replication requires a primer RNA.
- This precursor primer forms a persistent R loop during transcription in the mtDNA control region.
Purpose of the Study:
- To investigate if mammalian RNase mitochondrial RNA processing (MRP) can process R loops into replication primers.
- To determine if RNase MRP is sufficient for generating mtDNA leading-strand replication primers.
Main Methods:
- Formation of model R loops mimicking the physiological preprimer conformation.
- Incubation of R-loop substrates with mouse RNase MRP.
- Analysis of cleavage products to identify primer sites.
Main Results:
- Mouse RNase MRP effectively cleaved an R loop containing the mouse mtDNA origin.
- Cleavage sites on the R-loop substrate corresponded to known in vivo priming sites.
- RNase MRP demonstrated the capability to generate multiple primer sites.
Conclusions:
- RNase MRP is capable of processing R loops into functional primers for mtDNA replication.
- RNase MRP alone may be responsible for generating the majority of leading-strand replication primers in mammalian mitochondria.