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Biomedical subjects

M Crippa

Publications and source records attributed to M Crippa.

At least 73 records · Page 4Linked to original sources
PubMed1976

DNA-dependent RNA polymerase C from Xenopus laevis ovaries. Ability to transcribe intact double-stranded DNA.

DNA-dependent RNA polymerase C, partially purified from Xenopus laevis ovaries, has been resolved by DEAE-Sephadex chromatography in two forms, eluting at 0.2 M and 0.3 M ammonium sulfate, respectively. Both are sensitive to high concentrations of alpha-amanitin (200 mug/ml). Their ionic strength dependence and divalent cation requirements are indistinguishable. Quantitatively, RNA polymerase C represents the major form of RNA polymerase activity solubilized from the ovaries. Both RNA polymerases C are able to transcribe efficiently either high-molecular-weight Xenopus DNA or intact adenovirus DNA, as compared to nicked DNA. In contrast, RNA polymerase A has little activity on an intact DNA template. The salt dependence of the RNA polymerases C activity is different on the two kinds of template. Nicked DNA is efficiently transcribed up to a salt concentration of 100 mM ammonium sulfate. On intact DNA, optimal transcription is obtained at 40 mM ammonium sulfate and is inhibited by higher salt concentrations.

Amanitins↗
PubMed1972

An RNA-DNA complex intermediate in ribosomal gene amplification.

An RNA-ribosomal DNA complex can be isolated from ovaries of Xenopus laevis incubated in vitro during the amplification stage. A part of the RNA present in the complex is resistent to RNase but becomes completely sensitive after heat denaturation, a treatment that also allows the separation of the RNA from the DNA. The size of the RNA-ribosomal DNA complex is strongly reduced after treatment with RNase. A small fraction of the RNA present in the complex is complementary to the spacer region of the strand, which is not transcribed in vivo into cytoplasmic 18S and 28S ribosomal RNA.

Animals↗
PubMed1971

Synthesis of amplified DNA that codes for ribosomal RNA.

During the amplification stage in ovaries, the complete repetitive unit of the DNA that codes for ribosomal RNA in Xenopus appears to be transcribed. This large RNA transcript is found in a complex with DNA. Substitution experiments with 5-bromodeoxyuridine do not show any evidence that a complete amplified cistron is used as a template for further amplification. A derivative of rifampicin, 2',5'-dimethyl-N(4')benzyl-N(4')[desmethyl] rifampicin, preferentially inhibits the DNA synthesis responsible for ribosomal gene amplification. These results are consistent with the hypothesis that RNA-dependent DNA synthesis is involved in gene amplification.

Animals↗
PubMed1969

Maternal and embryonic contributions to the functional messenger RNA of early development.

Some of the DNA-like RNA synthesized during oögenesis remains available up to early blastula (stage 7). This RNA then begins to disappear from the embryo, so that by early gastrulation half of its sequences have been lost. Total maternal RNA of embryos represents more sequences than can be recovered at early stages from polyribosomes. Some of it must therefore reside in cytoplasmic fractions that do not cosediment with polyribosomes. Most of the maternal DNA-like RNA is eventually translated before it is lost. Messenger RNA transcribed on the embryonic genomes appears very early on polyribosomes and is translated there along with maternal RNA.

Animals↗