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E Beccari

Publications and source records attributed to E Beccari.

At least 37 records · Page 2Linked to original sources
PubMed1982

Expression of ribosomal-protein genes in Xenopus laevis development.

Using probes to Xenopus laevis ribosomal-protein (r-protein) mRNAs, we have found that in the oocyte the accumulation of r-protein mRNAs proceeds to a maximum level, which is attained at the onset of vitellogenesis and remains stable thereafter. In the embryo, r-protein mRNA sequences are present at low levels in the cytoplasm during early cleavage (stages 2-5), become undetectable until gastrulation (stage 10) and accumulate progressively afterwards. Normalization of the amount of mRNA to cell number suggests an activation of r-protein genes around stage 10; however, a variation in mRNA turnover cannot be excluded. Newly synthesized ribosomal proteins cannot be found from early cleavage up to stage 26, with the exception of S3, L17 and L31, which are constantly made, and protein L5, which starts to be synthesized around stage 7. A complete set of ribosomal proteins is actively produced only in tailbud embryos (stages 28-32), several hours after the appearance of their mRNAs. Before stage 26 these mRNA sequences are found on subpolysomal fractions, whereas more than 50% of them are associated with polysomes at stage 31. Anucleolate mutants do not synthesize ribosomal proteins at the time when normal embryos do it very actively; nevertheless, they accumulate r-protein mRNAs.

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PubMed1982

Nucleotide sequences of cloned cDNA fragments specific for six Xenopus laevis ribosomal proteins.

We have previously constructed and selected six recombinant plasmids containing cDNA sequences specific for different ribosomal proteins of Xenopus laevis (Bozzoni et al., 1981). DNA cloned in these plasmids have been isolated and sequenced. Amino acid sequences of the corresponding portions of the proteins have been derived from DNA sequences; they are arginine- and lysine-rich as expected for ribosomal proteins. One of the cDNA sequences has an open reading frame also on the strand complementary to the one coding for the ribosomal protein; this fragment has inverted repeats twenty nucleotides lone at the two ends. The codon usage for the six sequences appears to be non-random with some differences among the ribosomal proteins analysed.

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PubMed1981

Xenopus laevis ribosomal protein genes: isolation of recombinant cDNA clones and study of the genomic organization.

Poly-A+ mRNA from Xenopus laevis oocytes, partially enriched for r-protein coding capacity has been used as starting material for preparing a cDNA bank in plasmid pBR322. The clones containing sequences specific for r-proteins have been selected by translation of the complementary mRNAs. Clones for six different r-proteins have been identified and utilized as probes for studying their genomic organization. Two gene copies per haploid genome were found for r-proteins L1, L14, S19, and four-five for protein S1, S8 and L32. Moreover a population polymorphism has been observed for the genomic regions containing sequences for r-protein S1, S8 and L14.

Animals↗
PubMed1980

Messenger RNA for ribosomal proteins in Xenopus laevis oocytes.

Xenopus laevis oocytes (stage II--III) incorporate [35S]methionine into ribosomal proteins identifiable by two-dimensional electrophoresis. Poly(A)-rich RNA prepared form this source has been translated in a wheat germ cell-free system. Among the products synthesized in vitro 30 are clearly identifiable as ribosomal proteins. Some are not individually resolved, whereas a few of them may lack methionine or may not be correctly processed after the synthesis in vitro. An enrichment of our mRNA preparation for ribosomal protein activity can be obtained by subsequent passages on oligo(dT)-cellulose columns and by selection of a 10--16-S fraction by sucrose gradient sedimentation. We estimate that messenger RNA for ribosomal proteins represents 10--20% of this RNA preparation and can now be utilized for molecular cloning procedures.

Animals↗
PubMed1978

Clustered and interspersed repetitive DNA sequences in four amphibian species with different genome size.

We have compared the amount of clustered and interspersed repetitive sequences in the genome of four Amphibia with different DNA contents per haploid nucleus: two Anura (Xenopus laevis, 3 pg and Bufo bufo, 7 pg) and two Urodela (Triturus cristatus, 23 pg and Necturus maculosus, 52 pg). High molecular weight DNA of the four species was denatured and reassociated to the same Cot in order to obtain duplex sequences with a similar reiteration frequency. Single-stranded DNA was digested off with the Aspergillus S1 nuclease. DNA was then fractionated according to the molecular weight through an agarose A-50 column. We found that the amount of long repetitive sequences is roughly proportional to the genome size in the four species, while the number of short (about 300 base pairs) repetitive sequences is increased many-fold in the species with the larger DNA content, both in Anura and in Urodela.

Amphibians↗
PubMed1975

Isolation of a DNA fraction highly enriched in transfer RNA genes from Xenopus laevis.

A DNA fraction highly enriched in tRNA genes can be isolated from the Xenopus laevis genome by the use of Ag+/Cs2SO4 density gradients. Ag+ shows a low affinity for some tRNA cistrons, allowing their separation from bulk DNA upon equilibrium centrifugation in a Cs2SO4 density gradient. Contaminating DNA in the resulting tDNA fraction is further removed by two additional CsCl density gradient centrifugations. The final DNA fraction is 60-fold enriched in tRNA genes, compared to the starting DNA material.

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