title: Slower synthesis of individual replicons and adjacent replicon clusters in a radiosensitive xeroderma pigmentosum strain with and without X-irradiation.
abstract: Two replication parameters, synthesis of individual replicons and adjacent replicon clusters, were measured using DNA fiber autoradiography in a radiosensitive form of group C xeroderma pigmentosum (XP) XP2SP, in group C XP4SP, in group A Cockayne syndrome (CS) CS1SP and two normal human fibroblast strains. The novel observation here is that in non-irradiated XP2SP cells synthesis of individual replicons was significantly retarded as compared with all other cell lines tested and remained unchanged after 5-Gy X-rays. Also the number of simultaneously operating adjacent replicon clusters was uniquely reduced in only non-irradiated XP2SP cells and remained unaltered after 5-Gy irradiation. While the normal, XP4SP and CS1SP cells are radiosensitive to reduction in this replication parameter to a low level seen in both non-irradiated and 5-Gy irradiated XP2SP cells. Thus, non-irradiated XP2SP cells mimic irradiated normal, XP4SP and CS1SP cells. A possible relation of the above abnormalities in individual replicons and adjacent replicon clusters to a high incidence of spontaneous sister-chromatid exchanges and X-irradiation-induced chromosomal aberrations in XP2SP cells is discussed.
authors.affiliation: Institute of Cytology, Russian Academy of Sciences, St Petersburg.
authors.forename: L S
authors.initials: LS
authors.lastname: Barenfeld
authors.forename: S G
authors.initials: SG
authors.lastname: Nergadze
authors.forename: N M
authors.initials: NM
authors.lastname: Pleskach
authors.forename: V M
authors.initials: VM
authors.lastname: Mikhelson
mesh_terms: D002478:Cells, Cultured; D004261:DNA Replication; D006801:Humans; D066298:In Vitro Techniques; D012093:Replicon; D014965:X-Rays; D014983:Xeroderma Pigmentosum / Q000235:genetics*