title: Sister chromatid exchanges and inhibition of DNA synthesis in irradiated human cells.
abstract: X-ray irradiation inhibits DNA synthesis and enhances the frequency of sister chromatid exchanges (SCE) in normal human lymphocytes. On the contrary, cells from patients with Down's syndrome, Xeroderma pigmentosum (form II) and progeria, characterized by radioresistant DNA synthesis, do not show such an increase in SCE frequency. We suggest that radiation-induced SCE frequency is a result of inhibition of DNA replication, rather than a direct damage of chromosomes by ionizing radiation. It is in agreement with Painter's /13/ hypothesis according to which SCE are formed due to asynchronous completion of replication in contiguous replicon clusters. So, probability of SCE formation is the more the lower is rate of replication. Thus, the extent of radiation damage cannot be measured directly by the SCE frequency.
authors: Institute of Cytology, Academy of Sciences USSR, Leningrad.
authors: N M
authors: NM
authors: Pleskach
authors: M I
authors: MI
authors: Andriadze
authors: V M
authors: VM
authors: Mikhelson
authors: V D
authors: VD
authors: Zhestyanikov
mesh_terms: D004247:DNA / Q000096:biosynthesis*; D004261:DNA Replication / Q000528:radiation effects*; D004314:Down Syndrome / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000378:metabolism / Q000528:radiation effects / Q000648:ultrastructure; D011371:Progeria / Q000235:genetics / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics; D012854:Sister Chromatid Exchange / Q000528:radiation effects*; D014983:Xeroderma Pigmentosum / Q000235:genetics / Q000378:metabolism
chemical_list: D004247:DNA