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Biomedical subjects

J Avila

Publications and source records attributed to J Avila.

At least 271 records · Page 15Linked to original sources
PubMed1984

Antibodies to vimentin intermediate filaments in sera from patients with systemic lupus erythematosus.

Sera from patients with systemic lupus erythematosus and from healthy subjects were tested, using immunofluorescence and blotting techniques, for the presence of antibodies to intermediate filaments of the cytoskeleton of human skin fibroblasts. Both techniques showed that antibodies to intermediate filaments were found in a higher proportion of sera from patients (53%) than healthy subjects (9%). The antigen target was found to be the protein band that corresponded to vimentin (Mr 57,000).

Adolescent↗
PubMed1984

Characteristics of the binding of colchicine to porcine brain, cerebellum, pancreas, kidney, liver and spleen soluble protein: a comparative study.

Quantitative determination of tubulin levels present in the cytosol of different porcine organs was performed by a sensitive radioimmunoassay. The relationship between the amount of protein from liver or spleen and the colchicine bound was curvilinear, possibly due to the presence of an inhibitor of colchicine-tubulin binding in those organs. The rate of decay of colchicine binding increases when protein concentration decreases in brain, cerebellum, kidney and pancreas but it increases when protein concentration increases in liver and spleen.

Animals↗
PubMed1984

Involvement of the carboxyl-terminal domain of tubulin in the regulation of its assembly.

Limited proteolysis of phosphocellulose-purified tubulin with subtilisin resulted in cleavage of both alpha and beta tubulin subunits, with the formation of two major fragments (S alpha, and S beta, 48 kDa) and a small peptide (4 kDa) containing the carboxyl-terminal region of tubulin. Interestingly, tubulin cleaved under the present conditions showed an increased ability to assemble into large polymers in the absence of MAPs and under conditions that do not promote assembly of undigested tubulin--i.e., low magnesium concentrations and the absence of taxol and polyalcohols. The critical concentrations for the subtilisin-cleaved tubulin assembly was similar to that of MAPs-promoted tubulin assembly. Assembly product from subtilisin-cleaved tubulin consisted mainly of protofilament bundles, hooked polymer, and open tubules, structures showing equatorial and longitudinal spacings of 50 and 40 A, respectively. The existence of junctions between polymer walls indicates that the carboxyl-terminal removal facilitates polymer-polymer interactions. These results, together with previous studies on the involvement of the carboxyl-terminal domain of tubulin in its interaction with MAP-2, suggest a regulatory role for this domain in tubulin assembly. Thus, in general terms the tubulin molecule can be analyzed as a protein containing two essential domains with functional significance, one domain playing a major role in self-association and the other (the carboxyl-terminal moiety) playing a regulatory role in modulating the interactions responsible for self-association.

Animals↗
PubMed1981

Binding of microtubule protein to DNA and chromatin: possibility of simultaneous linkage of microtubule to nucleic and assembly of the microtubule structure.

Microtubule protein binds to DNA through microtubule associated polypeptides (MAPs). Among MAPs there is one high molecular weight polypeptide (MAP2) which interacts with DNA fundamentally through certain polynucleotide sequences. This interaction is not affected by the presence of histones and other chromosomal proteins. DNA can associate to assembled microtubules and when a determinate DNA/protein ratio is reached the nucleic acid behaves as a microtubule associated molecule. The nucleic acid fragments which preferentially bind to microtubules have been isolated and characterized. These fragments contain DNA regions enriched in repetitive sequences that hybridizes preferentially to the pericentromeric zone of metaphase chromosomes. These results give further support to the model of interaction microtubule-chromosome based upon the mediator function of the microtubule associated proteins.

Animals↗
PubMed1981

Factors implicated in determining the structure of zinc tubulin-sheets: lateral tubulin-tubulin interaction is promoted by the presence of zinc.

Addition of increasing amounts of zinc to a cold microtubule protein solution results in the disappearance of 30 S oligomer found in the absence of that cation and in the appearance of new tubulin oligomers, 90 S and 23 S. When a microtubule protein solution is warmed in the presence of zinc, tubulin-sheets are assembled. We have tested the influence of microtubule associated proteins and the zinc:tubulin ratio on the polymerization process. Depletion of microtubule associated proteins results in wider and longer tubulin-sheets than those polymerized in the presence of microtubule associated proteins. However by increasing zinc concentration wider but shorter tubulin-sheets were found. These results suggest that microtubule associated proteins and zinc could promote nucleation of tubulin-sheets, but zinc also promotes lateral tubulin-tubulin interaction. This interpretation was confirmed when microtubule protein was assembled at a low zinc:tubulin ratio. In such conditions composite structures of microtubules and zinc tubulin-sheets are formed. These composite structures are consequence of a lateral attachment of a zinc tubulin-sheet on a microtubule protofilament.

Animals↗
PubMed1981

Comparative measurement by radioimmunoassay of the brain microtubule-associated protein MAP2.

The presence of the microtubule-associated protein (MAP2) in the brain of several species has been investigated by SDS-gel electrophoresis and by radioimmunoassay. This assay had a sensitivity of approx. 10 ng and it was capable of measuring the protein either in purified microtubules or in crude brain extracts. As determined with this radioimmunoassay, MAP2 accounted for about 10% of the porcine brain microtubule protein and 1% of the protein from a brain extract. Taking porcine MAP2 as a reference, we have detected polypeptides with the same electrophoretic mobility in brain microtubules from cow, sheep, rat and chicken. Nevertheless, the MAP2 from these species showed a variable degree of immunoreactivity. Bovine MAP2 appeared closely related to the porcine protein whereas the rat antigen showed low cross-reaction and chicken MAP2 appeared immunologically unrelated to porcine MAP2. Our results suggest a higher variability of the MAP2 sequences as compared to that reported by other authors for the brain microtubule protein, tubulin.

Animals↗
PubMed1980

Incorporation of the high-molecular-weight microtubule-associated protein 2 (MAP2) into microtubules at steady state in vitro.

Purified high-molecular-weight microtubule-associated protein 2 (MAP2) labelled with [32P]-phosphate has been obtained and used as a marker to study the incorporation of this protein into microtubules at steady state in vitro. The incorporation kinetics of protein MAP2 show two different mechanisms of addition of this protein into microtubules. A fast incorporation, which proceeds essentially independently of microtubule assembly, indicates its addition into binding positions which may be available along the structure. Once the microtubule has been saturated with the protein, its incorporation proceeds from one end of the microtubule, in a polymerization-dependent manner, at a slower rate. Loss of the protein from microtubules at steady state proceeds fundamentally at the opposite end.

Animals↗
PubMed1980

Microtubule-associated-protein MAP1 is not implicated in the polymerization of microtubules.

Addition of DNA to microtubule protein solutions results in a decrease of the amount of the high-molecular-weight microtubule-associated proteins (MAP1 and MAP2) available for polymerization. Complete removal of MAP1 from microtubules requires lower concentrations of DNA compared to MAP2. Removal of MAP1 from microtubules has little or no effect on microtubule polymerization (nucleation and propagation). In contrast, removal of MAP2 produces a marked decrease in microtubule polymerization. Incubation of microtubular protein with DNA results in complete disappearance of the 30-S ring-shaped oligomers at concentrations of DNA which are not markedly inhibitory of polymerization.

Animals↗
PubMed1978

Separate effect of hydroxyurea on the initiation and elongation of DNA synthesis in BHK cells.

BHK21/Cl1 cells, starved for 30 h in serum deficient medium and treated for 15 h with 1 mM hydroxyorea (HO) in order to obtain a synchronous cell population in the G1/S-boundary, incorporate a residual proportion of 3H-thymidine (dThd). This residual incorporation is due to semiconservative synthesis and may not be reduced by increasing the drug concentration without affecting the reversion capacity of the cells proportionally. As shown by autoradiographic analysis, the residual DNA synthesis does not correspond to 3H-dThd incorporation within a small number of resistant cells, but is located in the nuclei of a high proportion of cells with reduced density of silver grains. After treatment with 0.05 mM HU, however, the incorporation of 3H-dThd increases considerably over the control values. The determination of the radioactivity incorporated by microgram DNA corresponding to nuclei in S phase indicates that this concentration of HU is also able to reduce the rate of DNA polymerization. Kinetic data on the appearance of this increased 3H-dThd incorporation and on the accumulation of labelled nuclei in cells growing at random and labelled continuously with the radioactive DNA precursor indicate that HU stimulates the cells to enter the S phase. The reported results are consistent with a mechanism of action of HU which affects initiation and elongation of DNA chains separately.

Cell Cycle↗