Biomedical subjects
Publications and source records attributed to A Alonso.
Incubation of cell-free extracts of C. utilis and its ethionine-resistant mutants with methionine, aspartate and alanine, and with various acceptor oxo-acids showed the presence of several transamination activities (Glu-Asp, Ala-Glu, Met-Glu, Met-Ala, Ala-Asp, but not Met-Asp). The lack of utilization of methionine by mec mutants appears to be due to a transport lesion.
A monoclonal antibody from clone T7 raised against total nuclear proteins from the Kc cell line of Drosophila melanogaster (Saumweber, H. Symmons. P. Kabisch, R. Will, H & Bonhoeffer, F, Chromosoma 80 (1980) 253) [1] showed positive immunofluorescent staining on interphase nuclei of HeLa and PTK2 cells. When this antibody was allowed to react with several nuclear protein fractions isolated from HeLa S3 cells, three polypeptides of molecular weights (MW) 44 000, 63 000 and 70 000 were identified as the corresponding antigens, all components of hnRNA containing ribonucleoprotein particles. Sucrose gradient fractionation of such particles after mild RNase treatment and subsequent analysis of the proteins by the immunoblotting method revealed that the 44 000 MW antigen was an integral part of the ribonuclease-resistant complex. The results support the view that hnRNA molecules are associated with certain proteins conserved during evolution which may play structural roles in the ribonucleoprotein organization.
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Of the RNA labelled after incubation of hepatoma cells with radioactive precursors for 20 and 150 min. 35% and 70%, respectively, can be isolated from nuclei by two consecutive extractions with 0.14 M NaCl at pH 8. The isolated RNA is complexed with nuclear proteins forming structures with sedimentation coefficients of less than 30 S to greater than 100 S. Similar complexes from rat liver isolated under the same experimental conditions show coefficients of 30-40 S. The RNA-associated proteins are similar, on the basis of sodium dodecyl sulphate/polyacrylamide gel electrophoresis, to the respective proteins of other cell types. The presence on these RNP complexes of six discrete small nuclear RNAs (snRNA) has been established. Experiments with a reversible inhibitor of RNA synthesis, D-galactosamine, demonstrated, differences in the turnover of hnRNA and snRNA. The half-lives of the six snRNA species has been determined, varying from 32 h for snRNA species a, b and d, to 22 h for snRNA species e and f and to 13 h for snRNA species c. Treatment of the nuclear extracts with 0.7 M and 1 M NaCl results in dissociation of hnRNA from the 'core' and other polypeptides, whereas snRNA remains complexed with polypeptides of Mr 54 000-59 000. Incubation of the nuclear extracts at 0 C with low doses of pancreatic R Nase (up to 1.5 micrograms/ml), which renders approximately 80% of the hnRNA acid-soluble and cleaves most of the snRNA, results in conversion of the high-molecular-weight hnRNPs to 30-S structures, without disrupting the 30-S RNP. Treatment of the nuclear extracts with higher doses of RNase (3 micrograms/ml) leads to disruption of the 30-S RNP and release of the hnRNA-associated proteins, underlining the importance of hnRNA-protein interaction for the retainment of the hnRNP structures.
Novikoff hepatoma cells have lost their capacity to synthesize albumin. As a first approach to study the mechanisms underlying this event, in vitro translation in a reticulocyte system was performed using total polyadenylated mRNA from rat liver and Novikoff hepatoma cells. Immunoprecipitation of the in vitro translation products with albumin-specific antibody revealed a total lack of albumin synthesis in Novikoff hepatoma, suggesting the absence of functional albumin mRNA in these cells. Titration experiments using as probe albumin cDNA cloned in pBR322 plasmid demonstrated the absence of albumin-specific sequences in both polysomal and nuclear polyadenylated and total RNA from Novikoff cells. This albumin recombinant plasmid was obtained by screening a rat liver cDNA library with albumin [32P]cDNA reverse transcribed from immuno-precipitated mRNA. The presence of an albumin-specific gene insert was documented with translation assays as well as by restriction mapping. Repression of the albumin gene at the transcriptional level was further demonstrated by RNA blotting experiments using the cloned albumin cDNA probe. Genomic DNA blots using the cloned albumin cDNA as probe did not reveal any large-scale deletions, insertions, or rearrangements in the albumin gene, suggesting that the processes involved in the suppression of albumin mRNA synthesis do not involve extensive genomic rearrangements.
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Based on the results of an ergometric stress testing performed in 22 patients with mitral replacement, the author concludes that this method is a highly reproductive and safe to evaluate the functional improvement of patients undergoing a mitral replacement. The results are similar for Bjork-Shiley (11 patients) and Starr-Edwards prothesis (11 patients), slurring that the only parameter that can affect functional results can be a controlled rehabilitation program.
The level of collaboration in phytohemagglutinin (PHA) induced lymphoblastic response by the macrophage of neonatal mice was studied. The results show a diminished response to the mitogen (PHA) when lymphocytes from the spleen of syngeneic adult mice were incubated in the presence of macrophages from neonatal mice as compared to those obtained from cultures performed in the presence of macrophages from adult mice. In both cases the highest response corresponded to the lowest dose of PHA and the lowest amount of macrophages used.
The association in young girls of flexion spasms of early beginning, partial or total agenesis of the corpus callosum, severe chororetinopathy and frequent skeletal anomalies is known as the Aicardi syndrome. On occasion of two observations a review of the literature is made.
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The present report describes the isolation of hnRNP complexes with sedimentation coefficients greater than 80 S from rat liver nuclei without the use of ribonuclease inhibitors. The RNA moiety from these complexes is heterogeneous in size, with a mean sedimentation coefficient of 16 S when assayed with polyacrylamide-formamide gel electrophoresis. About 3% of this RNA binds to oligo(dT)-cellulose, the size of the bound fraction being somewhat smaller than the bulk of the hnRNP-RNA. This poly(A) RNA contains two adenylate tracts, one with about 30 and the second with about 200 adenylate residues. Reverse transcription of the poly(A)-containing RNA and hybridization of the cDNA with their respective templates shows two well-defined frequency populations, the first one separated from the second by almost 2.5 logs in the R0t curve. The same distribution was found, whether the hybrids were analysed with S1 nuclease or hydroxyapatite. Both separated frequency classes hybridize to total genomic DNA, the abundant one at C0t values typical for repetitive and unique sequences, the scarce one only at C0t values typical for unique sequences. The two populations are also able to hybridize with polysomal polyadenylated mRNA, the dilution of both frequencies being very similar in the cytoplasm.
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A 8-month-old girl had an ependymoma in the clivus, 2 X 6 cm in size, connected with the fourth ventricle by a cord of tissue 0.5 cm thick. There were no indications to make us suspect the origin of the tumour in the fourth ventricle, or that it was a case of ependymoma.
Ethionine-resistant mutants of Candida utilis CCY-158 overproducing methionine have been isolated. In these mutants the intracellular methionine concentration decreased significantly during the stationary phase. The wild-type strain CCY-158 and the ethionine-resistant mutants isolated were able to use methionine as the nitrogen source but not as the carbon source. From these ethionine-resistant mutants we isolated mutants unable to use methionine as nitrogen source (Mec- mutants), the principal alteration being at the level of methionine uptake. Some of the Mec mutants lost also the ability to use other amino acids as nitrogen source.
The effect of a new synthetic C-nucleoside (2-beta-D-lyxopyranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one) on cell differentiation and growth was studied through three kinds of experiments: a) Appearance rate of peripheral blood cells in AKR mice, b) Growth capacity of Ehrlich ascite tumor cells and c) Reappearance rate of membrane receptors on T-lymphocytes which from E-rosette aggregates with sheep red cells. This C-nucleoside produced an inhibitory effect on all the processes studied, although not so strong as with the reference drug (methotrexate).
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