Abstract
Irradiation of DNA with UV light induces pyrimidine dimers and (6-4) photoproducts. The presence of one of these photolesions in the restriction site of a given endonuclease inhibits DNA cleavage and induces the formation of fragments by incomplete DNA digestion which appear as additional, facultative bands in Southern hybridization autoradiograms. The number and size of these fragments show a positive correlation with the UV dose. The response to UV light of immunoglobulin light-chain constant κ and heavy-chain constant μ genes was analyzed with 2 specific probes. Constant κ and μ genes when irradiated as part of the chromatin of living lymphocytes showed a UV sensitivity similar to that of naked DNA. The same genes from granulocytes had 50–60 times lower UV sensitivity. When cells were allowed to repair photolesions for 24 h the facultative bands from granulocytes disappeared indicating that these cells were able to remove photolesions from constant κ and μ genes. Facultative bands from lymphocytes showed a smaller decrease of density after 24 h repair. This suggests that lymphocytes are less efficient than granulocytes in removing UV damage from constant κ and μ genes.
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