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Metaphase chromatids are believed to consist of loops of chromatin anchored to a central scaffold, of which a major component is the decatenatory enzyme DNA topoisomerase II. Silver impregnation selectively stains an axial element of metaphase and anaphase chromatids; but we find that in earlier stages of mitosis, silver staining reveals an initially(More)
The enzyme DNA topoisomerase II, which removes the catenations formed between the DNA molecules of sister chromatids during replication and is a structural component of chromosome cores, is needed for chromosome condensation in yeast and in Xenopus extracts. Inhibitors of topoisomerase II arrest mammalian cells before mitosis in the G2 phase of the cell(More)
We have used synchronized HeLa cells to investigate the role of the nuclear membrane in preventing rereplication in a single cell cycle. Nuclei were prepared with intact nuclear membranes using streptolysin-O or digitonin and assayed for replication in Xenopus egg extracts. Intact G1 nuclei replicate semiconservatively, but intact G2 nuclei do not replicate(More)
We have investigated the mechanism which prevents reinitiation of DNA replication within a single cell cycle by exploiting the observation that intact G2 HeLa nuclei do not replicate in Xenopus egg extract, unless their nuclear membranes are first permeabilized (Leno et al., 1992). We have asked if nuclear membrane permeabilization allows escape of a(More)
BACKGROUND Methylating agents such as N-methyl-N-nitrosourea (MNU) can cause cell cycle arrest and death either via caspase-dependent apoptosis or via a poly(ADP-ribose) polymerase (PARP)-dependent form of apoptosis. We wished to investigate the possible role of MLH1 in signalling cell death through PARP. METHODS Fibroblasts are particularly dependent on(More)
The alkaline single-cell gel electrophoresis or comet assay is a relatively simple method of measuring DNA single-strand breaks and alkali-labile sites in individual cells. Previously, we have used a combination of this with bromodeoxyuridine labelling of DNA and immunolocalisation of the BrdUrd to show that DNA replicative integrity can be assessed in(More)
Thymidine kinase 1 (TK1) is a salvage enzyme that phosphorylates thymidine, imported from surrounding fluids, to create dTMP, which is further phosphorylated to the DNA precursor dTTP. TK1 deficiency has for a long time been known to cause increased cellular sensitivity to DNA damage. We have examined preferential strand break repair of DNA domains in(More)
Mitotic chromosome condensation is normally dependent on the previous completion of replication. Caffeine spectacularly deranges cell cycle controls after DNA polymerase inhibition or DNA damage; it induces the condensation, in cells that have not completed replication, of fragmented nuclear structures, analogous to the S-phase prematurely condensed(More)
Gene expression profiling by microarray technology has been successfully applied to classification and diagnostic prediction of cancers. Various machine learning and data mining methods are currently used for classifying gene expression data. However, these methods have not been developed to address the specific requirements of gene microarray analysis.(More)