DNA is replicated at the nuclear cage.

Structures resembling nuclei are released when HeLa cells are lysed in a detergent and 2 M salt. These nucleoids, which lack any organized membrane structure, contain all the nuclear DNA packaged within a cage of RNA and protein. Their DNA is supercoiled so that the linear DNA must remain unbroken and looped during lysis. Following digestion with the restriction endonuclease, EcoRI, cages and associated DNA were filtered free of unattached DNA. Pulse-labelled (i.e. newly synthesized) DNA remains preferentially associated with the cages. This association has been confirmed by autoradiography. When nucleoids are prepared for electron microscopy by the Kleinschmidt procedure the DNA spills out to form a skirt around the flattened cage. Labelling, which is restricted to the region of the cage after short pulses, extends out into the skirt as the labelling time increases. A model, based on the premise that replication takes place at the nuclear cage, is presented in the Appendix. The results of the biochemical experiments and electron microscopy both indicate that the average size of the unit of replication is approximately 2 micrometer. This is about one-quarter the size of the average structural unit - the loop. Therefore sequences in the loop must become attached to the nuclear cage prior to the initiation of DNA synthesis.

[1]  Peter R. Cook,et al.  Mapping sequences in loops of nuclear DNA by their progressive detachment from the nuclear cage , 1980, Nucleic Acids Res..

[2]  B. Vogelstein,et al.  A fixed site of DNA replication in eucaryotic cells , 1980, Cell.

[3]  P. Cook,et al.  Electron-microscopy of intact nuclear DNA from human cells. , 1979, Journal of cell science.

[4]  B. Jasny,et al.  Temporal organization of replication in DNA fibers of mammalian cells , 1979, The Journal of cell biology.

[5]  R. Hand.  Eucaryotic DNA: Organization of the genome for replication , 1978, Cell.

[6]  R. Sheinin,et al.  Some aspects of eukaryotic DNA replication. , 1978, Annual review of biochemistry.

[7]  J. Hamlin,et al.  Animal cell cycle. , 1978, Annual review of biochemistry.

[8]  P. Cook,et al.  Supercoiling of DNA and nuclear conformation during the cell-cycle. , 1978, Journal of cell science.

[9]  P. Cook,et al.  Spectrofluorometric measurement of the binding of ethidium to superhelical DNA from cell nuclei. , 1978, European journal of biochemistry.

[10]  P. Cook,et al.  The dissociation of nuclear proteins from superhelical DNA. , 1978, Journal of cell science.

[11]  H. Zachau,et al.  Domains in chromatin structure. , 1978, Cold Spring Harbor symposia on quantitative biology.

[12]  R. Wiegand,et al.  Uptake of homologous single-stranded fragments by superhelical DNA. IV. Branch migration. , 1977, Journal of molecular biology.

[13]  J. R. Paulson,et al.  The structure of histone-depleted metaphase chromosomes , 1977, Cell.

[14]  U. K. Laemmli,et al.  Role of nonhistone proteins in metaphase chromosome structure , 1977, Cell.

[15]  L. Povirk.  Localization of inhibition of replicon initiation to damaged regions of DNA. , 1977, Journal of molecular biology.

[16]  N. Cozzarelli.  The mechanism of action of inhibitors of DNA synthesis. , 1977, Annual review of biochemistry.

[17]  D. Comings,et al.  Nuclear proteins. III. The fibrillar nature of the nuclear matrix. , 1976, Experimental cell research.

[18]  A. Worcel,et al.  Isolation, characterization, and structure of the folded interphase genome of Drosophila melanogaster , 1976, Cell.

[19]  P. Cook,et al.  Characterization of nuclear structures containing superhelical DNA. , 1976, Journal of cell science.

[20]  H. Willard,et al.  Analysis of deoxyribonucleic acid replication in human X chromosomes by fluorescence microscopy. , 1976, American journal of human genetics.

[21]  R. Painter,et al.  Formation of nascent DNA molecules during inhibition of replicon initiation in mammalian cells. , 1976, Biochimica et biophysica acta.

[22]  H. Edenberg,et al.  Eukaryotic chromosome replication. , 1975, Annual review of genetics.

[23]  R. Painter,et al.  X-ray-induced inhibition of DNA synthesis in Chinese hamster ovary, human HeLa, and Mouse L cells. , 1975, Radiation research.

[24]  P. Cook,et al.  Supercoils in human DNA. , 1975, Journal of cell science.

[25]  J. Keller,et al.  The isolation and characterization of nuclear ghosts from cultured HeLa cells. , 1975, Biochemistry.

[26]  R. P. Aaronson,et al.  Isolation of nuclear pore complexes in association with a lamina. , 1975, Proceedings of the National Academy of Sciences of the United States of America.

[27]  R Berezney,et al.  Identification of a nuclear protein matrix. , 1974, Biochemical and biophysical research communications.

[28]  P. R. Cook,et al.  ON THE INHERITANCE OF DIFFERENTIATED TRAITS , 1974 .

[29]  P. Cook.  Hypothesis on Differentiation and the Inheritance of Gene Superstructure , 1973, Nature.

[30]  P. N. Rao.  Mitotic Synchrony in Mammalian Cells Treated with Nitrous Oxide at High Pressure , 1968, Science.

[31]  L. Caro,et al.  HIGH-RESOLUTION AUTORADIOGRAPHY , 1962, The Journal of cell biology.