title: Analysis of replicating DNA molecules from embryos of the sea urchin, Hemicentrotus pulcherrimus, by electron microscopy.
abstract: DNA was extracted from embryos of the sea urchin, Hemicentrotus pulcherrimus, at the S phase and examined by electron microscopy. We detected replication microbubbles with a mean size of 404 bases, in addition to replication macrobubbles of more than 1.0 kilobase (kb) in length. Seventy-five percent of the center-to-center distances of the microbubbles were 0.6-1.8 kb with a mean of 1.2 kb. Forty-five percent of the microbubbles were arranged as clusters of four or five microbubbles. These results suggest that at least 34% of the initiation sites for DNA replication are present on a DNA molecule in clusters in which the sites are arranged at 1.2-kb intervals.
mesh_terms: D000818:Animals; D004247:DNA / Q000648:ultrastructure*; D004261:DNA Replication; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology*; D007399:Interphase; D008854:Microscopy, Electron / Q000379:methods; D012617:Sea Urchins / Q000196:embryology
chemical_list: D004247:DNA