Within the human population, a significant proportion of individuals are unusually sensitive to ionising radiation. This is detected in the clinic when cancer patients are treated with radiotherapy. We are analysing cells from these individuals to see if they have a defect in repair of dsbs and if any of the proteins which carry out this repair are absent or abnormal. We have found such a defect in a leukaemic patient, who showed such an over-reaction to radiation treatment. A remarkable aspect of the responses of cells to DNA damage is that they are highly conserved throughout eukaryotes, i.e. exactly the same processes operate in single-celled yeasts and in man.
Simple yeasts are much easier to study than mammals and therefore provide excellent model systems.
Discoveries made with yeast systems can then be analysed in man. The combined use of yeast and mammalian systems provides a very powerful approach to analysing cellular processes. With the fission yeast system we are studying the response of the cell cycle to DNA damage. Normally a proliferating cell population needs to replicate its DNA and then partition the replicated chromosomes into two daughter cells. This must happen in strict and controlled order.