title: Electron microscopy of DNA replication in 3-D: evidence for similar-sized replication foci throughout S-phase.
abstract: DNA replication sites (RS) in synchronized HeLa cells have been studied at the electron microscopic level. Using an improved method for detection following the in vivo incorporation of biotin-16-deoxyuridine triphosphate, discrete RS, or foci are observed throughout the S-phase. In particular, the much larger RS or foci typically observed by fluorescence microscopic approaches in mid- and late-S-phase, are found to be composed of smaller discrete foci that are virtually identical in size to the RS observed in early-S-phase. Pulse-chase experiments demonstrate that the RS of early-S-phase are maintained when chased through S-phase and into the next cell generation. Stereologic analysis demonstrates that the relative number of smaller sized foci present at a given time remains constant from early through mid-S-phase with only a slight decrease in late-S-phase. 3-D reconstruction of serial sections reveals a network-like organization of the RS in early-S-phase and confirms that numerous smaller-sized replication foci comprise the larger RS characteristic of late-S-phase.
authors.affiliation: Department of Cell Biology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Albertov 4, CZ-12800 Prague 2, Czech Republic.
authors.forename: Karel
authors.initials: K
authors.lastname: Koberna
authors.forename: Anna
authors.initials: A
authors.lastname: Ligasová
authors.forename: Jan
authors.initials: J
authors.lastname: Malínský
authors.forename: Artem
authors.initials: A
authors.lastname: Pliss
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Siegel
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Cvacková
authors.forename: Helena
authors.initials: H
authors.lastname: Fidlerová
authors.forename: Martin
authors.initials: M
authors.lastname: Masata
authors.forename: Markéta
authors.initials: M
authors.lastname: Fialová
authors.forename: Ivan
authors.initials: I
authors.lastname: Raska
authors.forename: Ronald
authors.initials: R
authors.lastname: Berezney
mesh_terms: D004261:DNA Replication; D005453:Fluorescence; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008854:Microscopy, Electron; D016196:S Phase