ABSTRACT
Part of mitotic chromosome sets of the metaphase or anaphase SPEW mammalian cells were irradiated with an ultraviolet microbeam, and the subsequent incorporation of H3-thymidine into the postmitotic daughter nuclei was studied by autoradiography. The located areas of the unscheduled DNA synthesis were detected in these nuclei. This synthesis was likely to be due to repair process at the sites of postmitotic localization of the irradiated chromosomes. It is suggested that the selective chromosomal labeling induced by microirradiation could be employed in studying patterns of chromosome localization in the interphase nuclei. Local inhibition of the replicative DNA synthesis and local stimulation of the unscheduled DNA synthesis were observed after a partial microirradiation of the interphase nuclei. This unscheduled DNA synthesis was unaffected by hydroxyurea at concentration which inhibited normal DNA synthesis.
