Search results for "DNA Replication"
showing 7 items of 107 documents
Endoreduplication induced in cultured Chinese hamster cells by different anti-topoisomerase II chemicals
2005
With the ultimate purpose of testing the hypothesis that, as shown in yeast mutants, any malfunction of DNA topoisomerase II might result in aberrant mitosis due to defective chromosome segregation, we have chosen three chemicals of different nature, recently reported to catalytically inhibit the enzyme. The endpoint selected to assess any negative effect on the ability of topoisomerase II to properly carry out decatenation of fully replicated chromosomes in the G2/M phase of the cell cycle was the presence of metaphases showing diplochromosomes as a result of endoreduplication, i.e. two successive rounds of DNA replication without intervening mitosis. The anti-topoisomerase drugs selected …
Biochemistry and Molecular Biology of DNA Replication in Yeast
1985
For the past two decades, the study of the mechanism of DNA replication has been focused mainly on the chromosomes of the simple prokaryotes and their viruses (1). The complexity of the eukaryotic genome and multiple levels of control during the replication of eukaryotic chromosomes have until recently prevented similar studies. In recent years, a lower eukaryote, the yeast Saccharomyces cerevisiae, has become a major focus of efforts in molecular biology. In this chapter, I will briefly review accomplishments in this area. Yeast is an ideal model system for studies on the structure and replication of the eukaryotic chromosome. Yeast cells are easy to grow and study biochemically. Genetic a…
Expression of hMLH1 and hMSH2 proteins in ameloblastomas and tooth germs
2017
Background Mismatch repair proteins (MMRPs) are a group of nuclear enzymes that participate in the repair of base mismatches that occur during DNA replication in all proliferating cells. The most studied MMRPs are hMSH2 and hMLH1, which are known to be highly expressed in normal tissues. A loss of MMRPs leads to the accumulation of DNA replication errors in proliferating cells. Ki-67 is a biomarker regarded to be the gold-standard tool for determining cell proliferation by immunohistochemical methods. The aim of this study was to investigate the immunohistochemical expression of hMLH1, hMSH2 and Ki-67 proteins in ameloblastomas and tooth germs, to contribute to the understanding of the deve…
WRN protects against topo I but not topo II inhibitors by preventing DNA break formation
2008
The Werner syndrome helicase/3′-exonuclease (WRN) is a major component of the DNA repair and replication machinery. To analyze whether WRN is involved in the repair of topoisomerase-induced DNA damage we utilized U2-OS cells, in which WRN is stably down-regulated (wrn-kd), and the corresponding wild-type cells (wrn-wt). We show that cells not expressing WRN are hypersensitive to the toxic effect of the topoisomerase I inhibitor topotecan, but not to the topoisomerase II inhibitor etoposide. This was shown by mass survival assays, colony formation and induction of apoptosis. Upon topotecan treatment WRN deficient cells showed enhanced DNA replication inhibition and S-phase arrest, whereas af…
Cell Cycle: The Life Cycle of a Cell
2013
“Where a cell arises, there must be a previous cell”. This early statement of Rudolf Virchow already points to the process that is called cell cycle. It describes a series of events leading to cell division and duplication and can be sectioned into phases that are controlled by a collection of proteins interacting with each other, the cyclines and the cycline-dependent kinases. It is mandatory that DNA replication is conservative meaning that its structure and sequence remain unaltered while the DNA is duplicated before the cell actually divides. Checkpoints are responsible for the supervision, proteins such as p53 and RB being the key protagonists in cell cycle control. Upon DNA damage rec…
Growth factors and cell kinetics: a mathematical model applied to Il-3 deprivation on leukemic cell lines.
1992
We assume the existence of a specific G1 protein which is an initiator of DNA replication. This initiator is supposed to be synthesized according to Michaelis-Menten kinetics. In order to start DNA replication, it is assumed that this G1 specific protein must be produced in a required amount. Intra-cellular growth inhibitors and extra-cellular growth factors control the production of the initiator. This model allows to calculate the average G1 phase time as a function of the various chemical concentrations of nutrients, enzymes, growth inhibitors and growth factors. This model is compared to cell kinetics experiments on a leukemic cell line responding to Interleukin 3 deprivation. The curve…
Viral and cellular determinants of hepatitis C virus RNA replication in cell culture.
2003
Studies on the replication of hepatitis C virus (HCV) have been facilitated by the development of selectable subgenomic replicons replicating in the human hepatoma cell line Huh-7 at a surprisingly high level. Analysis of the replicon population in selected cells revealed the occurrence of cell culture-adaptive mutations that enhance RNA replication substantially. To gain a better understanding of HCV cell culture adaptation, we characterized conserved mutations identified by sequence analysis of 26 independent replicon cell clones for their effect on RNA replication. Mutations enhancing replication were found in nearly every nonstructural (NS) protein, and they could be subdivided into at …