title: Reversal of DNA polarity as revealed by sister chromatid exchanges in ring chromosomes.
abstract: DNA polarity at sister chromatid exchange (SCE) sites were studied in ring chromosomes from Chinese hamster cells. If the polarity of DNA strands was conserved. a double-length, symmetric dicentric ring chromosome with symmetric twin SCEs appeared after two cell cycles when a SCE occurred in S1. Indeed, approximately two-thirds of double-length. symmetric ring chromosomes belonged to this class. One-third of them, however, did not show symmetric SCEs, suggesting that polarity was not always conserved. SCE counts at centromeric regions were not high enough to account the frequency (about 1/3) of apparently inverted rejoining sites. The hypothesis that the polarity of rejoining sites is either conserved or inverted and that illegitimate rejoinings are partially repaired could explain the results. Telomere-like structures or intermediate structures during double-strand repair processes may contribute to the inverted polarity.
authors.affiliation: Itoham Central Research Institute, Ibaraki, Japan. sutou@fureai.or.jp
authors.forename: S
authors.initials: S
authors.lastname: Sutou
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000737:chemistry*; D012303:Ring Chromosomes; D012854:Sister Chromatid Exchange; D016615:Telomere
chemical_list: D004247:DNA