Repair of Chromosomal Damage

Early in the history of radiobiology repair of one type of X-ray induced genetic damage was inferred. This was the type of repair that is manifested as restitution of chromosome breaks. It was first postulated to account for the dose intensity or dose fractionation effect seen when chromosome exchanges were studied. This type of repair was found to require cellular metabolism and the production of ATP. Since the inhibition of protein synthesis also prevented repair it was postulated that the chromosomal bonds repaired were in protein. This point of view gains some credence from the lack of effect of DNA synthesis inhibitors, as well as from studies on the induction of aberrations by u. v. Whether or not the actual lesion induced by X-rays is a chromosome break, the data still indicate that repair of damage occurs and still give some dues about the nature of the damage and of the repair mechanisms. (author)