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F Solomon

Publications and source records attributed to F Solomon.

At least 37 records · Page 2Linked to original sources
PubMed1987

Domains of beta-tubulin essential for conserved functions in vivo.

The relationship between the primary sequence of tubulins and their properties in cells was studied by gene transfection experiments. Previously, we studied a chimeric beta-tubulin formed from chicken beta-tubulin-2 sequences in the amino-terminal portion and the highly divergent Saccharomyces cerevisiae TUB2 sequences in the carboxy-terminal 25% of the molecule. In the cytoplasm of cultured animal cells, this protein incorporates into all microtubule structures and assembles with the same efficiency as endogenous tubulin. We show that the protein products of chimeric genes with an increasing proportion of yeast sequence, extending 5' of the carboxy-terminal 25%, are abnormal in two ways. First, they assemble with a significantly lower efficiency than the original chimeric protein or the endogenous tubulins. Second, they are less stable in the cytoplasm. The results suggest that the position of the yeast sequences is crucial in determining the properties of the molecule. Results of analyses of 1 deletion mutation and 10 linker insertions in the original chimeric tubulin suggest that those changes made outside the carboxyl terminus completely disrupt assembly activity, while those made in the carboxyl terminus do not.

Alkaloids↗
PubMed1986

Two functional alpha-tubulin genes of the yeast Saccharomyces cerevisiae encode divergent proteins.

Two alpha-tubulin genes from the budding yeast Saccharomyces cerevisiae were identified and cloned by cross-species DNA homology. Nucleotide sequencing studies revealed that the two genes, named TUB1 and TUB3, encoded gene products of 447 and 445 amino acids, respectively, that are highly homologous to alpha-tubulins from other species. Comparison of the sequences of the two genes revealed a 19% divergence between the nucleotide sequences and a 10% divergence between the amino acid sequences. Each gene had a single intervening sequence, located at an identical position in codon 9. Cell fractionation studies showed that both gene products were present in yeast microtubules. These two genes, along with the TUB2 beta-tubulin gene, probably encode the entire complement of tubulin in budding yeast cells.

Amino Acid Sequence↗
PubMed1979

Sleeping pills.

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Anti-Anxiety Agents↗
PubMed1979

Identification with cellular microtubules of one of the co-assemlbing microtubule-associated proteins.

In this paper we describe a procedure for detecting proteins associated with cytoplasmic microtubules in vivo. Detergent-extracted cytoskeletons of NIL8 hamster cells are prepared under conditions which preserve the microtubules. The cytoskeletons are then extracted in the presence of calcium, which depolymerizes the microtubules and quantitatively extracted cytoskeletons are prepared from cells that have been incubated with colchicine. The cytoskeletons from these cells contain no microtubules or tubulin. Electrophoretic analysis of the calcium extracts of the colchicine-treated and untreated cells reveals several radioactively labeled polypeptides. There is, however, no apparent quantitative or qualitative difference between the two extracts other than the tubulin polypeptides. Each of the extracts is mixed with an excess of unlabeled calf brain microtubule protein and carried through cycles of temperature-dependent microtubule assembly. Distinct species from each extract co-assemble at a constant ratio, but only one polypeptide is uniquely derived from cells containing intact microtubules. The molecular weight of this polypeptide is similar to that proposed for the tau species detected in brain microtubule preparations.

Animals↗
PubMed1979

Detailed neurite morphologies of sister neurolbastoma cells are related.

Neuroblastoma cells exhibit a wide variety of patterns of neurite morphology. However, when these cells are induced to extend neurites under conditions in which mitotic sister cells are readily identifiable, 60% of these sister pairs display analogous morphologies. These cells are related either as identical twins or as mirror images of each other. The relatedness is expressed in considerable detail of neurite morphology. These relationshiops can persist through at least two cell divisions. The results suggest that animal cells can inherit specific determinants of shape.

Animals↗
PubMed1979

The outer boundary of the cytoskeleton: a lamina derived from plasma membrane proteins.

We prepared the cytoskeletal framework by gently extracting cells with Triton X-100. Lipids and soluble proteins were removed, leaving a complex meshlike structure which contains the cell nucleus and is composed of the major cell filament networks as well as the microtrabeculae with attached polyribosomes. The surface sheet or lamina covering this structure contains most of the cell surface proteins by the following criteria. Intact cells are labeled externally with radioiodine and then extracted with detergent. The iodinated poteins remain almost entirely with skeletal framework. A new major integral protein, the coat protein of Sindbis virus, is inserted into the plasma membrane of infected cells. This new protein is heavily iodinated and remains almost completely associated with the framework after extraction. Lectin binding and poliovirus binding sites are also retained after detergent extraction. Our results indicate that plasma membrane proteins form a sheet or lamina upon removal of lipids. This lamina reproduces even complex surface convolutions and appears to be supported by and intimately connected to the underlying skeleton. In this case, the surface lamina, and hence the plasma membrane of the original intact cell, might be viewed as a component of the cytoskeletal framework.

Animals↗
PubMed1979

Crawling movements of lymphocytes on and beneath fibroblasts in culture.

Some lymphocytes become highly motile upon immunological stimulation in vivo or in vitro. When introduced into a culture of 3T3 or L cells and followed by live-cell microscopy, some of these lymphocytes were observed to crawl on top of, along the edges of, and preferentially beneath the attached fibroblasts. The crawling could be as rapid as 20 mum/min, easily detectable without a time-lapse device. The striking ability of crawling lymphocytes to penetrate beneath attached 3T3 cells provided a quantitative means to compare the crawling activity of different lymphocyte populations under various conditions. Crawling was diminished by inhibitors of energy metabolism, by agents that disrupt the cytoskeleton, and by absence of Mg(2+) and Ca(2+), but not of Ca(2+) alone. Crawling lymphocytes were virtually absent in normal thymus and spleen cells. They increased greatly in 5-day mixed lymphocyte cultures and in peritoneal exudate lymphocytes taken after mice had been immunized with allogeneic tumor cells. T cells accounted for most of the crawlers. Of two T-cell leukemias tested, R1(+) cells were crawlers whereas EL-4 cells were not. The H-2 haplotype of the 3T3 fibroblasts (i.e., whether syngeneic or allogeneic) had no apparent effect on lymphocyte crawling activity. The crawling may relate to the exploration of cell surface antigens by lymphocytes (immune surveillance), to the mode of action of cytotoxic T cells, to the migration of lymphocytes across blood vessel walls, or to the penetration of lymphocytes into "solid" masses of normal tissue or tumor cells.

Animals↗
PubMed1978

A case of listeriosis in pregnancy with fetal survival.

Listeriosis during pregnancy is generally considered to result in an intrauterine infection which affects the fetus before birth or in the perinatal period. A case of listeriosis in a 38-yr-old diabetic woman with an influenza-like disease in her 32nd wk of pregnancy is presented. Two successive blood cultures were positive for Listeria monocytogenes type 4b and her serum showed a rising titer for agglutinins to this organism. After antibiotic treatment of the patient she gave birth to a healthy child.

Adult↗
PubMed1977

Binding sites for calcium on tubulin.

Calcium ions can inhibit the in vitro assembly of microtubules and, therefore, may play a role in the regulation of microtubule formation in vivo. In order to test the validity of this hypothesis; the interaction between calcium and pruified brain microtubular protein has been investigated by standard binding assays. We have detected and characterized two classes of binding sites for calcium on tubulin, the major component of cytoplasmic microtubules. There is a single high-affinity site per tubulin molecule, characterized by a dissociation constant of 3.2 X 10(-6) M. That site is inhibited by magnesium (k1 = 5 X 10(-5) M) and potassium chloride. There are approximately 16 low-affinity sites which have a dissociation constant of 2.8 X 10(-4) M, and which are also inhibited by potassium chloride. Binding at the low-affinity sites is slightly enhanced by low magnesium concentrations. Both classes of sites are distinguishable from the colchicine binding site, and are apparently also distinct from the vinblastine and guanine nucleotide sites. The characteristics of the calcium binding activity of tubulin are similar to those found for the calcium-binding proteins of sarcoplasmic reticulum. The results are consistent with a physiological role for calcium in the regulation of microtubule assembly.

Animals↗
PubMed1976

Utilization of the inactivation rate of coenzyme A transferase by thiol reagents to determine properties of the enzyme-CoA intermediate.

The rate of inactivation of succinyl-CoA:3-ketoacid coenzyme A transferase by thiol reagents is increased 3 to 100 times by very low concentrations of acyl-CoA substrates. The same maximum inactivation rate is found with acetoacetyl-CoA and succinyl-CoA. The enhanced rate of inactivation is caused by the stoichiometric formation of the enzyme-CoA intermediate and an accompanying conformation change of the enzyme. The inactivation rate provides a simple assay for the amount of enzyme present as the enzyme-CoA intermediate, using only catalytic concentrations of enzyme. This technique has been utilized to measure (a) a rate constant for hydrolysis of the enzyme-CoA intermediate of 0.10 min-1 at pH 8.1; (b) a stoichiometry of two active sites per enzyme molecule; and (c) the equilibrium constants for formation of the enzyme-CoA intermediate from dilute solutions of substrates (and hence for the overall reaction) by determining the ratio of [enzyme-CoA]/[enzyme] in the presence of a series of substrate "buffers" at different ratios of [RCOO-]/[RCOSCoA]. As the total concentration of acyl-CoA and carbosylate substrates is increased, the inactivation rate is decreased. This indicates that the Michaelis complexes are protected against inactivation.

Binding Sites↗