Response to X-ray- and cis Pt-induced DNA damage in (Ciliata, Protozoa)

The macronuclei of the ciliated protozoan Stylonychia lemnae are highly resistant to several DNA-damaging agents, but the micronuclei are sensitive. Possible reasons for these differences were investigated. Although both kinds of nuclei continue to synthesize DNA and repair damage after application of Cisplatin, the micronuclear division rate slows down, and its DNA is degraded. Apparently only the macronuclei repair damage successfully. After treatment with X-rays, the micronuclei are lost because they are unable to divide. In the macronucleus no recombination repair was found. Our hypothesis is that the macronucleus can survive because it has enough copies of each gene to cope with the loss of some of them.