Ian Holt group

Mitochondrial DNA Replication and Expression

Small circles of DNA are maintained in mitochondria (mitochondrial DNA), the major energy producing compartment of the cell.

The Human Mitochondrial Genome

The Human Mitochondrial Genome

Click image to view at full-size

Mitochondrial DNA of humans encodes 13 components of the respiratory chain and ATP synthase (these genes are shown in green, blue, red and pale yellow).

Loss of function of mitochondrial DNA gives rise to a broad range of human diseases, and it is increasingly recognised as an important factor in common disorders, such as diabetes mellitus and late-onset neurodegeneration. To maintain their DNA, mitochondria operate a unique mechanism of replication entailing the incorporation of RNA on the lagging strand template, as leading strand DNA synthesis proceeds. We have recently identified the source of the RNA and next aim to elucidate the means by which it is incorporated during mitochondrial DNA replication. Specifically - what are the key proteins involved, and what are the consequences for the mitochondrial genome if RNA incorporation is blocked?

Replication intermediates of mitochondrial DNA contain RNA.

Replication intermediates of mitochondrial DNA contain RNA.

Click image to view at full-size

To resolve and visualise replicating molecules of mitochondrial DNA we separate them on agarose gels and hybridize to radiolabelled pieces of DNA. The image shows two gels superimposed. Green represents intermediates where the associated RNA has been removed, using the enzyme RNase H. Yellow arcs and spots are species unaffected by the enzyme treatment and so lack RNA, whereas red areas correspond to species that contain RNA.

To help to address these questions we have identified many new proteins that interact with mitochondrial DNA and are developing screening strategies to determine their impact on mitochondrial DNA metabolism. These studies dovetail with the laboratory’s other major interest: the organisation and segregation of mitochondrial DNA and how this impacts on cell and organ function, and ultimately human health.

Mitochondrial DNA Maintenance

Mitochondrial DNA Maintenance

Click image to view at full-size

Many proteins associate with mitochondrial DNA to regulate its replication, maintenance and expression. In the depicted human osteosarcoma cells the DNA has been stained with pico-green dye. Mitochondrial DNAs are the small green foci surrounding the large green area of the nucleus.

Selected publications

Our research themes

Click links to view others working on these themes

Top of page

© MRC National Institute for Medical Research
The Ridgeway, Mill Hill, London NW7 1AA