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Cell. 2002 Nov 15;111(4):495-505.

Biased incorporation of ribonucleotides on the mitochondrial L-strand accounts for apparent strand-asymmetric DNA replication.

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  • 1MRC-Dunn Human Nutrition Unit, Hills Road, CB2 2XY, Cambridge, United Kingdom.


Recently, we presented evidence for conventional, strand-coupled replication of mammalian mitochondrial DNA. Partially single-stranded replication intermediates detected in the same DNA preparations were assumed to derive from the previously described, strand-asymmetric mode of mitochondrial DNA replication. Here, we show that bona fide replication intermediates from highly purified mitochondria are essentially duplex throughout their length, but contain widespread regions of RNA:DNA hybrid, as a result of the incorporation of ribonucleotides on the light strand which are subsequently converted to DNA. Ribonucleotide-rich regions can be degraded to generate partially single-stranded molecules by RNase H treatment in vitro or during DNA extraction from crude mitochondria. Mammalian mitochondrial DNA replication thus proceeds mainly, or exclusively, by a strand-coupled mechanism.

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