Differential replication capacities of G1 and S-phase extracts from sea urchin eggs

1993 ◽  
Vol 104 (2) ◽  
pp. 565-572
Author(s):  
H. Zhang ◽  
J.V. Ruderman
Keyword(s):  
Dna Synthesis ◽  
Sea Urchin ◽  
Nuclear Dna ◽  
Specific Pattern ◽  
S Phase ◽  
Sperm Chromatin ◽  
G1 Arrest ◽  
Sea Urchin Eggs ◽  
Egg Extracts ◽  
Fertilized Egg

Sea urchin eggs are arrested in G1 of the first mitotic cell cycle. Fertilization triggers release from G1 arrest and the onset of DNA synthesis about 20 minutes later, even when protein synthesis is blocked. Here we describe extracts from eggs and S-phase embryos that reproduce this stage-specific pattern of DNA synthesis. Fertilized egg extracts formed nuclear membranes around decondensed Xenopus sperm chromatin whereas unfertilized egg extracts did not. Aphidicolin-sensitive deoxynucleotide incorporation was high in extracts of fertilized S-phase eggs and low in those of unfertilized eggs. In contrast, single-stranded DNA templates directed high rates of incorporation in both unfertilized and fertilized egg extracts, suggesting that the stage-specific activities in nuclear DNA synthesis is restricted to initiation on double-stranded DNA. Mixing experiments showed that unfertilized eggs do not contain a dominant inhibitor of replication, nor does fertilization induce the appearance of a soluble, dominant activator.

scholarly journals LIMITED DNA SYNTHESIS IN THE ABSENCE OF PROTEIN SYNTHESIS IN PHYSARUM POLYCEPHALUM

1966 ◽  
Vol 31 (3) ◽  
pp. 577-583 ◽  
Author(s):  
J. E. Cummins ◽  
H. P. Rusch
Keyword(s):  
Protein Synthesis ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Physarum Polycephalum ◽  
Nuclear Dna ◽  
S Phase ◽  
Early Prophase ◽  
Late Prophase ◽  
Removal Experiments ◽  
Inhibitor Of Protein Synthesis

Actidione (cycloheximide), an antibiotic inhibitor of protein synthesis, blocked the incorporation of leucine and lysine during the S phase of Physarum polycephalum. Actidione added during the early prophase period in which mitosis is blocked totally inhibited the initiation of DNA synthesis. Actidione treatment in late prophase, which permitted mitosis in the absence of protein synthesis, permitted initiation of a round of DNA replication making up between 20 and 30% of the unreplicated nuclear DNA. Actidione treatment during the S phase permitted a round of replication similar to the effect at the beginning of S. The DNA synthesized in the presence of actidione was replicated semiconservatively and was stable through at least the mitosis following antibiotic removal. Experiments in which fluorodeoxyuridine inhibition was followed by thymidine reversal in the presence of actidione suggest that the early rounds of DNA replication must be completed before later rounds are initiated.

DNS-Synthese in frühen Furchungsstadien von Seeigelembryonen / DNA-Synthesis in Early Cleavage Stages of Sea Urchin Embryos

1970 ◽  
Vol 25 (9) ◽  
pp. 1047-1052 ◽  
Author(s):  
G. Czihak ◽  
E. Pohl
Keyword(s):  
Dna Synthesis ◽  
Sea Urchin ◽  
Incubation Time ◽  
Transport Mechanism ◽  
Nuclear Dna ◽  
Incorporation Rate ◽  
Thymidine Uptake ◽  
Early Cleavage ◽  
Single Nucleus ◽  
Cleavage Stages

Incorporation rate of thymidine into nuclear DNA of cleaving sea urchin eggs is independent of the incubation time before fertilization. The incorporation rate into the single nucleus was found to be higher in later cleavage stages than immediately after fertilization. A constant value is reached after a certain time. Thymidine uptake is considered to be dependent on a transport mechanism starting with fertilization.

scholarly journals Cell population heterogeneity in the inducibility of DNA synthesis in human diploid fibroblasts.

1981 ◽  
Vol 89 (2) ◽  
pp. 194-197 ◽  
Author(s):  
M V Rao
Keyword(s):  
Dna Synthesis ◽  
Cytochalasin B ◽  
Nuclear Dna ◽  
S Phase ◽  
Population Heterogeneity ◽  
Diploid Fibroblasts ◽  
Binucleate Cells ◽  
Human Diploid Fibroblasts ◽  
Significant Difference ◽  
Sister Cells

The initiation of nuclear DNA synthesis has been studied in cytochalasin B (CB)-induced binucleate human diploid fibroblasts (WI-38 cells). Mitotic cells from different passage levels were rendered binucleate by a brief pulse of CB. The cells were then washed free of the drug, and DNA synthesis was studied by [3H]thymidine labeling. The results showed that, in a small percentage of binucleate cells, one nucleus was labeled (S phase) and the other nucleus was unlabeled (G1 phase). There was no significant difference in the percentage of these cells with increasing passage levels. The results of this study suggest that some WI-38 cells retire from the cell cycle at different passage levels, and thereby become refractory to inducers of nuclear DNA synthesis generated by sister cells in S phase.

scholarly journals INDEPENDENCE OF CENTRIOLE FORMATION AND DNA SYNTHESIS

1973 ◽  
Vol 57 (2) ◽  
pp. 359-372 ◽  
Author(s):  
J. B. Rattner ◽  
Stephanie G. Phillips
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Temporal Relationship ◽  
Nuclear Dna ◽  
S Phase ◽  
Centriole Duplication ◽  
And Migration ◽  
Cellular Dna ◽  
Arabinosyl Cytosine ◽  
Mitotic Cells

The temporal relationship between cell cycle events and centriole duplication was investigated electron microscopically in L cells synchronized by mechanically selecting mitotic cells. The two mature centrioles which each cell received at telophase migrated together from the side of the telophase nucleus distal to the stem body around to a region of the cytoplasm near the stem body and then into a groovelike indention in the early G1 nucleus, where they were found throughout interphase. Procentrioles appeared in association with each mature centriole at times varying from 4 to 12 h after mitosis. Since S phase was found to begin on the average about 9 h after mitotic selection, it appeared that cells generated procentrioles late in G1 or early in S. During prophase, the two centriolar duplexes migrated to opposite sides of the nucleus and the daughter centrioles elongated to the mature length. To ascertain whether any aspect of centriolar duplication was contingent upon nuclear DNA synthesis, arabinosyl cytosine was added to mitotic cells at a concentration which inhibited cellular DNA synthesis by more than 99%. Though cells were thus prevented from entering S phase, the course of procentriole formation was not detectibly affected. However, cells were inhibited from proceeding to the next mitosis, and the centriolar elongation and migration normally associated with prophase did not occur.

Autoradiographic evidence for the effects of light on RNA and DNA synthesis during chloroplast replication in spores of Polytrichum

1977 ◽  
Vol 28 (1) ◽  
pp. 61-70
Author(s):  
L.B. Kass ◽  
D.J. Paolillo
Keyword(s):  
Dna Synthesis ◽  
Nuclear Dna ◽  
Acid Synthesis ◽  
S Phase ◽  
Temporal Separation ◽  
Dark Incubation ◽  
Chloroplast Replication ◽  
Rna And Dna Synthesis ◽  
Rna And Dna ◽  
Stimulation Of

Light stimulates the incorporation of [3H]uridine and [3H]thymidine in addition to plastid replication in germinating Polytrichum spores. Significant amounts of [3H]uridine and [3H]thymidine are incorporated in darkness but not to the same level as in light. Plastids continue to produce nucleic acids when their capacity to multiply is suspended due to the absence of light. However, a higher amount of DNA synthesis in the light is correlated with the result that chloroplast replication begins again in the light after prolonged dark incubation. An imperfect association of plastid replication and nucleic acid synthesis is suggested by the lack of stimulation of DNA synthesis by light during plastid replication in the first 8 h of incubation. A temporal separation can be demonstrated for chloroplast and nuclear DNA synthesis at the beginning of germination in Polytrichum spores, with DNA synthesis in the chloroplasts preceding that in the nucleus. The mitotic S phase is longer than 16 h for at least half of the nuclei.

Regulation of Cdc2/cyclin B activation by Ran, a Ras-related GTPase

1995 ◽  
Vol 108 (3) ◽  
pp. 1217-1225 ◽  
Author(s):  
P.R. Clarke ◽  
C. Klebe ◽  
A. Wittinghofer ◽  
E. Karsenti
Keyword(s):  
Translational Control ◽  
Nuclear Dna ◽  
Bound State ◽  
Inhibitory Effect ◽  
S Phase ◽  
Cyclin B ◽  
Mutant Form ◽  
Nucleotide Exchange ◽  
Free System ◽  
Egg Extracts

During the cell cycle, a checkpoint prevents the initiation of mitosis until S-phase is completed. The molecular mechanism may involve the RCC1 protein, which catalyses guanine nucleotide exchange on the Ras-related nuclear protein, Ran (or TC4). Genetic studies have suggested that RCC1 may be involved in sensing the replication state of DNA and controlling the activation of Cdc2/cyclin B protein kinase through Ran. In this report, we present direct biochemical evidence for the post-translational control of Cdc2/cyclin B activation by Ran. In a cell-free system of concentrated Xenopus egg extracts supplemented with nuclei, a mutant form of Ran (T24N) analogous to dominant inactive mutants of other Ras-related GTPases inhibits Cdc2/cyclin B activation in the presence of replicating nuclear DNA. This role for Ran is mediated through control of the tyrosine phosphorylation state of Cdc2 and appears to be distinct from other effects on nuclear import, nuclear formation and DNA replication. When extracts were supplemented with RCC1 protein prior to addition of Ran T24N, inhibition of Cdc2/cyclin B by Ran T24N was relieved. This suggests that Ran T24N may act in a dominant manner by sequestering RCC1 in an inactive form. In contrast to Ran T24N, a mutant of Ran (Q69L) defective in GTPase activity and hence locked in the GTP-bound state has no inhibitory effect on Cdc2/cyclin B activation. In the light of these results, we propose that generation of the GTP-bound form of Ran is required for Cdc2/cyclin B activation and entry into mitosis when this process is coupled to the progression of S-phase.

scholarly journals Variations in the phosphate content and thiol/disulphide ratio of histones during the cell cycle. Studies with regenerating rat liver and sea urchins

1968 ◽  
Vol 107 (3) ◽  
pp. 403-410 ◽  
Author(s):  
Margery G. Ord ◽  
L A Stocken
Keyword(s):  
Dna Synthesis ◽  
Sea Urchin ◽  
Rat Liver ◽  
Sea Urchins ◽  
Phosphate Content ◽  
Γ Irradiation ◽  
Sea Urchin Eggs ◽  
Regenerating Rat Liver ◽  
S Period

1. In regenerating rat liver the phosphate content of the lysine-rich histone F1, but not that of the more arginine-rich histone F3-1, increases during the period of DNA synthesis. 2. The phosphorylation of histone F1 in this ‘S period’ is decreased by γ-irradiation, but, like phosphate uptake into DNA, is affected to an even greater extent if the irradiation is given in the presynthetic period. 3. Histones from three species of sea-urchin eggs show similarities to the F2 and F3 groups of histones from mammalian thymus gland. 4. The proportion of thiol to total thiol plus disulphide in acid extracts from sea-urchin eggs varies from less than 20% in mature unfertilized eggs to 59% just before cleavage. 5. The phosphorylated forms of histones F1 and F3 are less effective in decreasing DNA synthesis by DNA polymerase than the non-phosphorylated forms. 6. Oxidation of thiol groups on histone F3-1 does not affect its capacity to decrease DNA synthesis in vitro.

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