title: Deoxyribonucleic acid replication in fetal cells.
abstract: OBJECTIVE
  Our purpose was to develop a sensitive method for assessing the replication time of specific human genes in cultured fetal cells and for detecting potential replication defects.
  
  
  METHODS
  Synchronous progression of diploid human fetal lung cells through S phase was achieved by releasing from serum restriction with minimum essential medium alpha modification plus 10% fetal bovine serum, followed by hydroxyurea blockage at the G1/S boundary. Deoxyribonucleic acid replication was studied in permeabilized cells using mercurated nucleotides to label nascent deoxyribonucleic acid.
  
  
  RESULTS
  A high degree of synchrony in traversal of S phase was indicated by flow cytometry and a well-defined 7-hour period of deoxyribonucleic acid synthesis. The replication of the topoisomerase II gene occurred in a narrow time span 3 hours after entry into S phase.
  
  
  CONCLUSIONS
  Fetal cells have been highly synchronized at the beginning of S phase, and the replication time of a specific gene can be defined within a narrow time window.
authors.affiliation: Department of Metabolic Regulation, Boston Biomedical Research Institute, Massachusetts.
authors.forename: T
authors.initials: T
authors.lastname: Sagesaka
authors.forename: N
authors.initials: N
authors.lastname: Boubnov
authors.forename: T
authors.initials: T
authors.lastname: Okuyama
authors.forename: H
authors.initials: H
authors.lastname: Paulus
authors.forename: N
authors.initials: N
authors.lastname: Sarkar
mesh_terms: D002453:Cell Cycle / Q000502:physiology*; D002478:Cells, Cultured; D003584:Cytological Techniques; D004247:DNA / Q000096:biosynthesis; D004261:DNA Replication; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004171:Diploidy; D005260:Female; D005333:Fetus / Q000166:cytology*; D005347:Fibroblasts / Q000166:cytology; D005434:Flow Cytometry; D006801:Humans; D008168:Lung / Q000166:cytology; D008297:Male; D016196:S Phase / Q000502:physiology*
chemical_list: D004247:DNA; D004250:DNA Topoisomerases, Type II