When activated by near-ultraviolet light, 8-methoxypsoralen can react with pyrimidine bases to produce mono-adducts in DNA. Upon further irradiation these mono-adducts can be converted to interstrand crosslinks, but if the re-irradiation is carried out in the absence of unbound 8-methoxypsoralen, no new mono-adducts can be formed. The effects of re-irradiation are, therefore, a consequence of the conversion of mono-adducts into crosslinks. Here we report the types of chromosomal aberrations produced by re-irradiation and, hence, by DNA crosslinks. Our results demonstrate that crosslinks induce a wide variety of chromosomal aberrations in the first division after treatment. In addition, crosslinks are shown to induce new aberrations in second-division cells, a result which shows that the crosslink or some lesion derived from it survives at least one round of DNA replication.
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