[A theoretical model of structural chromosome rearrangement induction]

A theoretical model to explain the occurrence of chromosome rearrangements at the DNA molecular level is proposed. It involves: (10) breakage of one strand of each DNA molecule; (20) enzymatic digestion by an exonuclease of a short sequence of bases adjacent to the lesion, hence the presence of a short monocatenar segment on the complementary strand; (30) association of two monocatenar sequences if they are sufficiently complementary hence the formation of an X-shaped heteroduplex; (40) repair synthesis of DNA and, during this repair, an exhange of strands identical to that occuring in sister-chromatid exchanges, hence the rearrangement. This model has the advantage of necessitating one single breakpoint per DNA molecule, and explains the efficiency of radiations with low linear transfer of energy, such as X- and gamma-rays. It also explains how rearrangements such as translocations can be totally balanced since they would occur base to base within identical sequences.