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Biomedical subjects

M Méchali

Publications and source records attributed to M Méchali.

63 records · Page 4Linked to original sources
PubMed1983

Induction of chromosome replication during maturation of amphibian oocytes.

After fertilization amphibian embryos replicate their chromosomes faster than bacteria replicate their much smaller chromosomes. During oogenesis, materials are accumulated to sustain these rapid cycles of chromosome replication. Thus growth is uncoupled from nuclear division. Most of the machinery for DNA replication and chromatin assembly is present in the oocyte, which lacks only the ability to initiate on a DNA duplex. After maturation and activation a cell cycle clock is triggered which specifies initiation of DNA replication on endogenous chromosomes, injected nuclei or injected plasmid DNA. The ability to reinitiate replication of a replicated molecule is tightly coupled to the cell cycle clock. Each egg can replicate an amount of DNA equivalent to 500 diploid nuclei in only five hours. However, each egg can assemble an amount of purified DNA equivalent to 12 000 diploid nuclei into regularly spaced nucleosomes in only one hour. The molecular basis of these extraordinary rates of DNA replication and chromatin assembly is considered.

Animals↗
PubMed1983

Tumor promoter TPA increases initiation of replication on DNA injected into xenopus eggs.

The effect of the tumor promoter TPA on the control of DNA replication was assayed by following the regulated replication of DNA microinjected into eggs of the frog Xenopus laevis. TPA increases the amount of replication of injected DNA. Both initiation of replication on parental DNA molecules and reinitiation on previously replicated molecules are stimulated. Interaction with the external membrane appears necessary since injections of high concentrations of TPA into the egg are ineffective, whereas nM concentrations are active in the external medium. Related molecules that lack tumor promoting activity do not affect DNA replication. The effect of TPA on DNA replication was detectable only after the first cell cycle, and TPA cannot induce replication in oocytes, the quiescent stage which precedes the egg. When protein synthesis is inhibited TPA still increases initiation of replication, but does not allow detectable reinitiation cycles. The results suggest that interaction of TPA with the cell membrane is sufficient to increase the efficiency of replication initiation by a mechanism that does not require illegitimate reinitiation within a single cell cycle.

Animals↗
PubMed1982

DNA synthesis in a cell-free system from Xenopus eggs: priming and elongation on single-stranded DNA in vitro.

We describe a eucaryotic in vitro system for DNA replication derived from Xenopus eggs. In this system, priming and elongation of DNA chains occurs with unusually high efficiency on single-stranded circular DNA templates. Up to 1.5 micrograms M13 DNA can be converted to a completely double-stranded form by 100 microliters egg extract in 1 hr at 22 degrees C, a rate of synthesis comparable with the fastest rates of chromosomal DNA synthesis in early embryogenesis. Initiation of DNA synthesis on double-stranded circular DNA templates was undetectable however. The enzymatic events responsible for complementary-strand synthesis in vitro resemble those presumed to act at the lagging strand of the eucaryotic replication fork in vivo in three ways. First, inhibitor studies indicate that DNA polymerase alpha is required. Second, priming of DNA synthesis by oligoribonucleotides is strongly supported by the complete dependence on ribonucleoside triphosphates in the assay, and the detection of an oligoribonucleotide terminus of 9 or possibly 10 nucleotides associated with nascent DNA chains. Third, the priming reaction is resistant to alpha-amanitin.

Amanitins↗
PubMed1977

DNA polymerase activities in growing cells infected with simian virus 40.

Growing CV1 cells were infected with simian virus 40 (SV40), and the levels of DNA polymerases-alpha, -beta, and -gamma were analyzed in the cytoplasm, nuclear Triton wash, and nucleus. In the cytoplasmic fraction, the amount of alpha-, beta-, or gamma-polymerase remained unaltered after SV40 infection. The activity of DNA polymerase-alpha increased five- to sixfold in the nuclear Triton wash and threefold in the nuclei and then remained enhanced only inside the nuclei. That of DNA polymerases-beta and gamma increased mostly in the nuclei after infection. These results suggest that DNA polymerase-alpha could be the major enzyme involved in SV40 DNA replication.

Cell Line↗