Possible mechanisms of chromosome aberrations. 1. The patterns of UV-induced aberrations

In initial asynchronous culture of embryonic fibroblasts of BALB line mice a study was made on chromosomal aberrations in the first mitosis after UV-radiation at 254, 265, 280 and 302 nm wave lengths with doses from 2 up to 10 J/m2 in G1, S and G2 periods. In accordance with time of realization in mitotic cycle two classes of aberrations, one of which is realized before prometaphase, beginning (probably, in interphase) and the other - during metaphase, were distinguished. It was established that aberrations of the 1st class occur at the same constant frequency in about 7% of cells regardless of the period of mitotic cycle, radiation dose and wave length. It was concluded that they appear in the result of indirect effect of UV-radiation on chromosomes; the mechanism of their occurance is independent of the intensity of dna replication synthesis. The aberrations of the 2d class do not occur during irradiation in G2 period, and in G1 and S periods they comprise the suppressing number of aberrations and determine the character of cytogenetic effect of UV-radiations as a whole. Their frequency increases linearly with the growth of radiation dose; UV-spectrum of action for them coincides with thymidine adsorption spectrum and spectrum of action for cross links of dna. It points to the leading role of interchain links of dna in their initiation and important role of replication synthesis of dna in their realization