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A five-year programme of research led by a team of scientists at the University of Sussex has resulted in significant breakthroughs in our understanding of how enzymes that make DNA help to replicate damaged genomes.

In three related studies, the researchers looked at whether a particular group of enzymes that make DNA called primases, found in both lower organisms, such as bacteria, as well as in humans, plays significant roles in DNA repair processes in cells.

In the first of these studies, the team, led by Professor Aidan Doherty and his colleagues in the Genome Damage and Stability Centre,  have identified how bacterial primases are able to bridge DNA breaks and fill-in gaps, thus allowing the  integrity of the genome to be restored. These findings have major implications for our understanding of the unprecedented roles of such enzymes in DNA repair processes that are commonly disrupted during the development of major diseases related to genome instability, such as cancer.

These studies led them to investigate if related primases also play important roles in DNA repair in human cells and this resulted in the discovery a previously unidentified human primase called  PrimPol. The Doherty group found that if the PrimPol  gene is knocked out of cells then the genome is replicated much more slowly. They went on to show that one of the major roles of  human PrimPol is to enable the cell’s DNA replication machinery to bypass DNA damage, such as UV lesions,  that would otherwise act as a molecular “roadblock”, obstructing genome duplication.

They also looked at the role it plays in the skin cancer condition, xeroderma pigmentosa (XP). It is already known that cells deficient in another repair enzyme, Pol Eta, develop XP. The researchers found that disrupting PrimPol in XP cells makes them much more sensitive to sunlight damage, resulting in even slower DNA replication. This suggests  that PrimPol-associated mutations, like Pol Eta, are likely to make cells more sensitive to DNA damaging agents and contribute to the development of human diseases, such as cancer.

Finally, in a closely related study, the researchers studied the role PrimPol plays in trypanosomes. These are simple protozoan parasites that cause a range of diseases in sub-Saharan Africa and South America, such as the severely debilitating conditions known as sleeping sickness and chagas. They found that knocking out PrimPol from trypanosomes prevented them from replicating their genomic DNA and therefore causing them to die. In common with human PrimPol, the parasitic enzyme is required to enable cells to replicate though damaged DNA.

PrimPol is also found in a range of other major human pathogens, such as plasmodium that causes malaria.

Professor Doherty says: “This early work indicates that this enzyme is a potentially promising target to develop novel drugs to treat these conditions. Although PrimPol is essential for replication of these parasites, it is not essential for human cell viability, thus minimising potential side effects from potential PrimPol inhibitors.”

The work was funded by grant support from the BBSRC and MRC and is being published in the journals Molecular Cell and Cell Reports in November 2013.

Notes for editors

The research has led to the publication of three papers:

• ‘Molecular basis for DNA double-strand break annealing and primer extension by a NHEJ DNA polymerase’Nigel C. Brissett1§, Maria J. Martin2§, Edward J. Bartlett1, Julie Bianchi1,Luis Blanco2, Aidan J. Doherty1* Cell Reports  (14 November 2013)
  
• ‘PPL2 translesion polymerase is essential for the completion of chromosomal DNA replication in the African trypanosome’. Rudd, S., Glover, L., Jozwiakowski, S.K., Horn, D., & Doherty, A.J.
  Molecular Cell  (21 November 2013) 
  
• ‘PrimPol bypasses UV photoproducts during eukaryotic chromosomal DNA replication’. Bianchi, J., Rudd, S. Jozwiakowski, S.K., Bailey, L., Soura, V., Taylor, E., Green, A.J., Stracker, T.H.
  Lindsay, H.D. &  Doherty, A.J.  
  Molecular Cell (21 November 2013)