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J Smarda

Publications and source records attributed to J Smarda.

At least 55 records · Page 3Linked to original sources
PubMed1987

Viroids: molecular infectious agents.

In 1971, unique small RNA molecules, the viroids, were found to cause specific infectious diseases of plants. They are the smallest and simplest contagious agents known. Until now, 14 viroids have been described and 12 diseases of potatoes, tomatoes, citruses, chrysanthemums, cucumbers, hops, coconut palms avocado trees and burdock are known to be caused by viroids. The common symptoms of these diseases are: stunting of plants. discoloration of veins, epinasty, curling and distortions of leaves, chlorotic or necrotic spots etc., followed by death of the diseased plants. All viroids are ssRNAs of m.w. ranging from 1.1 x 10(5) to 1.7 x 10(5), corresponding to chains of just 246 to 371 ribonucleotides. For 10 viroids, complete nucleotide sequences are known PSTV, CSV, CEV, TPMV and TASV show 60%-80% homology with each other; in analogy, ASBV, HSV, CPFV. GV and CCCV are closely homologous to each other, too, but just distantly related to the PSTV group. Extensive intramolecular base pairing creates a characteristic secondary structure of the cyclic viroid RNA chain, native viroids appearing as quasi double-stranded, unbranched, very short rod-like structures with short single-stranded loops. (Thus PSTV forms rods about 50 nm long and 2 nm wide.) The stretch of nearly all viroids bears a common central conserved region of 19 bp. The "upper" part of this region is, presumably, the cleavage-ligation site of viroid oligomers during replication. Viroids are located and replicated in nuclei of infected cells, in association with their nucleoli. Their replication is directed by host DNA-dependent RNA polymerase II using cRNA oligomers as templates according to the rolling circle model. Viroid RNA has no mRNA function. The virulence of viroids is coded by their virulence modulating region in the "left hand" part of their molecules: a single nucleotide substitution between nucleotides 43 and 56 within this region alters the virulence. Most probably, viroids have originated by the circularization of spliced-out transcripts of eucaryotic introns. A stable complex may be created between the 5' end of U1 snRNA and nucleotides 257 to 279 of PSTV cRNA strand; thus the pathogenic effects of viroids seem to be a result of their interference with pre-mRNA processing.

Base Sequence↗
PubMed1987

Production of bacteriocin-like agents of Budvicia aquatica and "Pragia fontium".

In cultures of 9 budvicia aquatica and 5 "Pragia fontium" strains production of distinct bacteriocin-like agents was proved. It is suggested to call them aquaticins and fonticins. They display strain specific antibacterial activities towards both genera; however, they are not active towards Escherichia coli or Shigella sonnei indicators. Their inhibition zones are conspicuously narrow (turbid or clear). Their spontaneous production may be enhanced by UV-induction of producing bacteria. They are readily set free into the medium; no intracellular accumulation occurs. With only one exception, they are trypsin-resistant and remarkably heat-sensitive, being damaged at 45 degrees C to 55 degrees C. All these results suggest that aquaticins and fonticins are of corpuscular character. This assumption was proved true by electron microscopic observation of one of the fonticins: this resembles contracted tails of bacteriophage T4.

Bacteriocins↗
PubMed1985

Studies of colicin action on wall-less stable L-forms of Escherichia coli. II. Growth inhibition of complete and wall-less (L-form) cells of Escherichia coli by basic colicin types.

The inhibitive activity of colicins of 16 types (produced by 22 colicinogenic strains) on rods and protoplast-like stable L-form cells of the strains Escherichia coli B, W1655 F+ and W1655 F- was compared. The results of 58 combinations tested fall into four groups (with three subgroups): both cell forms are sensitive: a) both cell forms are about equally sensitive, b) rods are distinctly more sensitive than L-form cells, c) L-form cells are distinctly more sensitive than rods; only rods are sensitive, L-form cells are not sensitive; only L-form cells are sensitive, rods are not sensitive; neither cell form is sensitive. Group la represents simple sensitivity; both cell wall and cytoplasmic membrane receptors are present and functioning. Groups 1b and 2 represent sensitivity, substantially or completely mediated by cell wall receptors. Groups 1c and 3 represent partial or complete "pseudoresistance" or "pseudotolerance"; cell wall receptors are absent or non-lethal, but cytoplasmic membrane ones are present and mediate the lethal effect. Group 4 represents both true resistance and true tolerance.

Colicins↗
PubMed1985

Studies of colicin action on wall-less stable L-forms of Escherichia coli. III. A colicin-tolerant mutant in a wall-less stable L-form.

The conversion of a tol III Escherichia coli mutant, tolerant to colicins E2, E3, Ia and K, into protoplast-like stable L-form makes it sensitive to colicins E2, Ia and K. Its original sensitivity to colicin E1 and tolerance to E3 are preserved in this cell form. Thus, rods of this mutant are not truly tolerant to colicins E2, Ia and K, but "pseudotolerant": their wall receptors have been turned out to "nonlethal" ones by the mutation in question.

Colicins↗
PubMed1979

Effect of colicin E3 on leukemia cells P388 in vitro.

Proliferation of murine leukemia cells P388 is stimulated by less than 1.0 mg/ml colicin E3, while being inhibited by higher concentrations. By 1.6 mg/ml colicin E3, uptake of thymidine into cold TCA-precipitable fraction is decreased by 59% during 24 h, uptake of uridine by 29%.

Animals↗
PubMed1979

Studies of colicin action on wall-less stable L-forms of Escherichia coli. I. Degree of attachment and of killing effect on rods and stable L-form cells.

Escherichia coli strains B and K12 W 1655 F+ are able to bind more lethal units of colicins E2, E3, G, H, Ia, and K+ X per one stable L-form cell (of the protoplast type) than per one rod cell; colicin D is bound in a higher amount on E. coli B rods. This pattern remains unchanged, if the same colicins are attached on chloroform-killed cells of both forms. Rods of both E. coli strains are more sensitive to colicins D, E2, E3, K + X (as--in the strain B--to colicin Ia) than cells of the respective L-forms. In the strain W 1655 F+ both cell forms are equally highly sensitive to colicin Ia. The stable L-forms of both strains are much more sensitive to colicins G and H than the rods. Thus the Gram-negative cell wall decreases the probability of a colicin molecule to get attached to its receptor in the cytoplasmic membrane. On the other hand, in E. coli cells the attachment of most colicin molecules to the wall receptors increases the probability of their biological effect. There is no such effect of the wall-attachment on the action of colicins G or H. The strain B is tolerant to colicin E2, while being resistant to E3; thus the cytoplasmic membrane receptor sites for them are not identical.

Adsorption↗
PubMed1979

The cytoplasmic membrane as a site of the primary effect of colicins on eukaryotic cells.

The effect of colicins E3 and K on mouse lymphoid cells was studied. Low doses of colicin E3, which were not toxic, inhibited profoundly the Con A-induced activation of lymphocytes while the Con A binding capacity of the treated cells was retained. The inhibitory effect of colicin E3 was also found when the homing of 51Cr-labelled lymph node cells to the lymph nodes of syngeneic recipients was studied, while the rate of redistribution of H-2 antigens on the surface of the lymphocytes was not changed by colicin E3 or colicin K. The findings suggest that the cytoplasmic membrane is the site of the primary effect of colicin E3 on eukaryotic cells.

Animals↗
PubMed1978

The cytotoxic and cytocidal effect of colicin E3 on mammalian tissue cells.

The plasma membrane of mammalian cells can mediate the cytotoxic and cytocidal effects of colicin E3. As little as 10(2) lethal units of purified colicin E3 per cell exert a pronounced cytocidal effect on human epithelial HeLa cells and as little as 10(4) lethal units per cell also on line L mouse fibroblasts in tissue culture. Cells in complete monolayers are rapidly killed, become spherical and shrink, they are detached from the support and finally autolyzed. The percentage of killed cells in both lines is directly proportional to the multiplicity of colicin used. The LD50 for HeLa cells is about 30 times lower than for L cells. At the multiplicity of 10(5) I.u., usually 100% HeLa and 90% L cells are killed in 2--3 days. Purified colicins E2 and D have no demonstrable cytological effect on HeLa cells, although DNA synthesis in L cells appears to be partly inhibited by colicin E2. The profound effect of colicin E3 on mammalian cells could be interpreted in a similar way as in bacteria, viz. as a specific cleavage of rRNA.

Cell Adhesion↗
PubMed1975

Novel approaches to the mode of action of colicins.

According to the theory of Fredericq (1949) and Nomura (1964), colicins are attached by specific receptor sites in the cell walls of sensitive bacteria, which mediate their inhibitive effects. During last years, a great variety of experimental data have been accumulated, some of which cannot be easily interpreted in terms of this theory. There exist considerable discrepancies concerning the chemical nature and molecular weight of isolated receptors. The attachment of a colicin onto its receptor need not be irreversible. The inhibition of numerous membrane-associated functions in colicin-tolerant mutants suggests their pleiotropic deletion nature. The difference between colicin resistance and colicin tolerance does not seem to be clear-cut. Cells of stable L-forms of protoplast type, completely devoid of their walls, retain in most cases the same patterns of sensitivity to colicins as rods of the same strains. Experimental changes in the relationship between the cell wall and the cytoplasmic membrane decrease colicin sensitivity of the cells. Colicin E3 has been found to be a specific endoribonuclease, able to cleave a terminal fragment from the 16 S rRNA also in isolated ribosomes in vitro: not only in ribosomes from sensitive bacteria, but also in those from resistant ones and from eukaryotic cells. A destabilization of the DNA helix was induced by colicin E2 in vitro as in vivo. It seems that there exist two distinct types of colicin receptors with different functions: those in the cell wall, and those in the cytoplasmic membrane. Only the contact of colicins with the latter ones is biologically effective and starts both stages of their inhibitive effect: the reversible and the irreversible ones.

Bacteria↗