Stabilization of a miniderivative of the broad-host-range IncW plasmid pSa by insertion of plasmid R1parB region

The plasmid vector pEM100 (13.5 kb) constructed from pGV1106, a miniderivative of the broad-host-range IncW pSa plasmid, and the pAM330 plasmid ofBrevibacterium lactofermentum is not stably maintained inEscherichia coli host cells under nonselective growth conditions. By insertion of a 0.9 kb DNA fragment containing theparB locus (responsible for the maintenance of plasmid R1 inE. coli cells) to plasmid pEM100, plasmid pEM110 was prepared which is maintained in a population ofE. coli cells growing without a selection pressure very stably. Translated by Č. Novotny     

Analysis of a model for antagonistic muscles

In the present work a linear model for a pair of antogonistic muscles is analysed. Each constituent muscle in this model is identical to ones considered previously (Stein and Ouztöreli, 1976). Analytical properties of the antagonistic muscles and dynamics of the system are described and some numerical results are discussed. The natural modes of the system are determined by a fourth order polynomial, which most commonly has one pair of conjugate complex roots and two negative real roots. The filtering of neural inputs through the active state properties of the muscle increases the order of the system to fifth order for these inputs.This work was partly supported by the National Scientific and Engineering Research Council of Canada Grant NRC-A4345 and by the Medical Research Council of Canada Grant MRC-MT-3307 through the University of Alberta     

Response analysis of vertebrate retina

In a recent work (Ouztöreli, 1980) a mathematical model for studying the neural activities in a vertebrate retina has been investigated, where the basic network contains five interconnected neurons: a receptor cell, a bipolar cell, a horizontal cell, an amacrine cell, and a retinal ganglion cell. More recently, in (Ouztöreli and O'Mara, 1980) the basic network has been extended to a larger network containing twelve neurons. In both of these works, the performances of the basic and extended models were discussed under different structural and processing conditions with constant inputs by using the results of one of our earlier work (Ouztöreli, 1979). In the present paper we investigate by simulations the responses of the basic retinal network to piecewise constant and periodic inputs. The step and frequency responses of the extended retinal network will be discussed in a forthcoming paper.This work was partially supported by the Natural Sciences and Engineering Research Council of Canada under Grant A-4345 through the University of alberta     

Nucleotide sequence encoding the 5'' end of Xenopus laevis 18S rRNA.

We have sequenced a region of cloned Xenopus laevis ribosomal DNA encompassing the last 24 nucleotides of the external transcribed spacer and the first 275 nucleotides of the 18S gene. The start of the 18S gene was identified by correlating the results obtained from RNA hybridization and fingerprinting with the DNA sequence. This 5' region of 18S rRNA contains five 2'-O-methyl groups and at least six pseudouridine residues. Several of these modified nucleotides are clustered into a relatively short region from nucleotides 99-124. Nucleotides 227-250 constitute a distinctive sequence of 24 consecutive G and C residues. Comparison with the first 160 nucleotides of a yeast 18S gene (25) reveals three blocks of high sequence homology separated by two short tracts where homology is low or absent. The external transcribed spacer sequences diverge widely from within a few nucleotides of the start of the 18S gene.     

Some effects of the induction of gametogenesis in the populations of the homothallic algaChlamydomonas geitleri Ettl

The induction of gametogenesis in the studied homothallic alga by the transfer to a nitrogen-Less medium leads to an adaptation of the cell population until a dynamic equilibrium is attained. Throughout the adaptation, the homeostatic forces regulating the number of the cells in the population assert themselves on the basis of internal nitrogen circulation. Part of the induced cells which perform no conjugation is probably destroyed by lysing, whereas the cells being just in the pre-Induction phase as well as those having passed the phase without being induced to gametes, continue their cycles by means of the released nitrogenous substances. The conditions which in some cells cause the induction of gametogenesis, produce a partial spontaneous synchronisation in other cells. The course of the cell cycles in parts of the culture may be determined according to the pulses of the increasing number of the zygotes within the whole cell population, if the cell cycles have run at a certain degree of synchrony. The culture conditions which induce gametogenesis cause a quick decrease of the biosyntheses of the RNAs while the biosyntheses of the DNAs are almost maintained at the original level. During the dynamic equilibrium of the population, the average content of the RNAs per cell remains very low, whereas the average content of the DNAs per cell virtually does not change (compared with the original state).     

Injection of mitochondria into oocytes and fertilized eggs]

The suspension of mitochondria isolated from the loach embryos or the frog heart were injected in the oocytes or fertilized eggs of the loach, newt, toad and frog in the amount roughly equivalent to the content of mitochondria in the egg. After the injection the oocytes did not differ during several days from the normal ones and the fertilized eggs of the loach, newt and South Afican clawed toad developed normally. The activity of cytochrome oxidase in the injected oocytes was kept at a somewhat higher level (1.4 to 1.9 vs 1.0 in the control) during several days. In the developing eggs the activity of cytochrome oxidase began to decrease from the blastula stage and attained rapidly the control level. The decrease of the enzyme activity is due to non-specific degradation of excessive mitochondria or to compensatory inactivation of the enzyme ensuring the maintenance of its normal activity during the development.     

Sensitization of three strains of chlorococcal algae for UV- effects by 5- bromodeoxyuridine

The sensitization of chlorococcal algae by 5-BdU for the purpose of UV-light mutagenesis was studied. The results obtained were compared with our earlier findings on the sensitization of the same algal strains by 5-BU. No shielding effect of the 5-BdU molecules against UV-light was observed. Probably, the uptake of them from the liquid medium did not result in such excess as compared with the treatment by 5-BU, even if the cells were long enough (24 h) exposed to the concentration of 5-BdU. Likewise, neither stimulating nor inhibiting growth effects on the growing cell colonies were observed after treatment with 5-BdU. The sensitization of the algal cells for UV-light effects was effective in all the experiments. An increased damage of the algal cells by UV-light after sensitization was proved in all the parameters recorded. The frequencies of permanent changes of the cells or their colonies were also increased, but their spectrum did not change significantly. A suitable combination of the 5-BdU sensitization of the cells before their influencing by UV-light and the induction of their repair mechanisms by visible light may decrease the frequencies of the lethal or sublethal damage and increase the frequencies of the useful permanent changes in the characteristics of the chlorococcal algae. The results obtained are discussed from the viewpoint of the regulated mutation process in the breeding of algae.     

The Concanavalin A agglutinating system of cell membranes.

The hopes raised by the finding of differential Concanavalin A (Con A) agglutinability of normal and transformed cells in efforts to quantify differences between these cell lines seem not to have been justified. In this paper, the development of information on the mechanism of action of Con A on the cell surface, as well as the theories put forward at each stage of this development are surveyed. In this respect, investigations on Con A constitute a case history in biological research. The involvement of glycoproteins and galactosyltransferases in cell-cell interactions and their relations to Con A are also reviewed.     

GoFigure: automated Gene Ontology annotation

SUMMARY: We have developed a web tool to predict Gene Ontology (GO) terms. The tool accepts an input DNA or protein sequence, and uses BLAST to identify homologous sequences in GO annotated databases. A graph is returned to the user via email. AVAILABILITY: The tool is freely available at: http://udgenome.ags.udel.edu/frm_go.html/