Molecular mechanisms of the origin of chromosome aberrations and the structural organisation of eukaryotic DNA

The rejoining of DNA double-strand breaks and a model for the formation of chromosomal rearrangements

The recombination type of process, which has been proposed by Resnick to explain the rejoining of radiation-induced DNA double-strand breaks, is combined with the molecular theory of radiation action to provide a description of the formation of chromosomal rearrangments. It is shown that the majority of chromosomal aberration types found at the first mitosis after radiation can be explained on the basis of one radiation-induced DNA double-strand break in the backbone of the unineme chromatid, followed by the enzymatically controlled recombinational process for the rejoining of the double-strand break. The recombinogenic process for the repair of DNA double-strand breaks relies on the close association between the broken DNA double helix and homologous DNA. The homologous nature of repeated DNA base pair sequences is used, in this model, to explain the occurrence of chromosomal exchanges between non-homologous chromosomes. The important role which repetitive DNA plays in the formation of chromosomal rearrangements and in the distribution of 'break-points' found in radiation experiments is discussed.