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Biomedical subjects

G Magnusson

Publications and source records attributed to G Magnusson.

At least 127 records · Page 7Linked to original sources
PubMed1984

A medical record and information system for primary health care in Iceland. The Egilsstadir Project.

In Iceland a problem oriented medical record system for primary health care has been developed. A contact-form is used to record data on all contacts between the inhabitants in a district and the health center. A minicomputer is used for retrieval and analysis. One rural health center using this system has been successful in recording a basic set of data on all contacts taking place since 1976 and linking these data to the national register data for the population in the district. Most health centers in Iceland are now adopting this system, because it seems to be: A valuable aid in the treatment of patients, which improves the quality of the treatment. A useful source of information of the health of the population, which among other things makes possible the identification of those at special risk. A good instrument for research and teaching. A useful source of statistics on the primary care services.

Humans↗
PubMed1983

Identification of an active disaccharide unit of a glycoconjugate receptor for pneumococci attaching to human pharyngeal epithelial cells.

Glycoconjugates containing the disaccharide unit GlcNAc beta 1 leads to 3Gal beta were suggested as receptors for pneumococci adhering to human pharyngeal epithelial cells. The receptor activity was detected both by inhibition of adhesion by an excess of free oligosaccharide and by induction or increase of adhesion after coating of target cells with glycolipid. Studies with free natural and synthetic oligosaccharides identified the disaccharide GlcNAc beta 1 leads to 3Gal beta as one critical binding site. The specificity of recognition was shown inter alia by the lack of inhibitory activity of GlcNAc beta 1 leads to 4Gal beta, which differs only in the linkage of the two sugars. Specific interference with pneumococcal adhesion by administration of soluble receptor sugar may improve our understanding of the role of adhesion in vivo.

Animals↗
PubMed1983

High efficiency polyoma DNA transfection of chloroquine treated cells.

Chloroquine treatment of rodent cells during the first hours of polyoma DNA transfection increase the fraction of cells expressing viral functions. The effect has been observed after DNA absorption using both the DEAE-dextran and calcium phosphate coprecipitation methods. Exposure to chloroquine increased the proportion of transfected mouse cells to approximately 40%. From a culture of one million such cells, microgram quantities of newly synthesized viral DNA could be isolated. Similarly, the transformation frequency of rat cells following polyoma DNA transfection was approximately 6-fold increased by chloroquine treatment. The effect of the compound was even more pronounced in transfections with linear forms of polyoma DNA, suggesting that chloroquine inhibits degradation of DNA absorbed by the cells.

Animals↗
PubMed1983

T-antigen expression by polyoma mutants with modified RNA splicing.

Polyoma virus mutants were constructed that could not express all the three T-antigens. The mutagenesis was directed to the two 5' splice sites utilized in the maturation of early RNA. The mutant bc1051 had a base change at the splice site of large T-antigen mRNA, and the mutants dl1061 and dl1062 had deletions at the corresponding splice point of small and middle T-antigen mRNA. The site was removed in mutant dl1061 and altered by fusion to upstream sequences in mutant dl1062. Analysis of viral RNA showed that dl1061 and dl1062 formed only large T-antigen mRNA, whereas bc1051 did not produce this RNA-species. However, the biological properties of dl1062 suggested that it also produced mRNA directing the synthesis of a small T-antigen-related polypeptide, at least in low amounts. Only mutant bc1051 could induce transformation of rat cells. In mouse 3T3 cells dl1062 multiplied to a limited extent, while bc1051 and dl1061 failed to produce virus. However, dl1061 DNA was synthesized at a low rate which could be increased to normal levels by co-transfection with mutant bc1051. This result suggests that polyoma small and middle T-antigen have a previously unrecognized function in the early phase of the infection process, or in viral DNA-synthesis.

Antigens, Viral, Tumor↗
PubMed1983

Deletion mapping of a short polyoma virus middle T antigen segment important for transformation.

Viable polyoma virus mutants were constructed that had small deletions in the early region of the genome. The deletions together removed most of the segment missing from the genome of the nontransforming mutant dl23 (N. Smolar and B. E. Griffin, J. Virol. 38:958-967, 1981). The transformation properties, as measured by colony formation in soft agar, of mutants with overlapping or contiguous deletions showed that part or all of the middle T antigen segment, consisting of the short amino acid sequence Glu4-Tyr-Met-Pro-Met, was essential for the activity of the protein in transformation. However, the segment could be deleted without significant effect on the in vitro protein kinase activity associated with the middle T antigen.

Antigens, Viral↗
PubMed1983

Molecular mechanisms of adhesion of Streptococcus pneumoniae to human oropharyngeal epithelial cells.

Adherence of bacteria to mucosal surfaces is an early step in colonization and infection. Streptococcus pneumoniae colonizes the nasopharynx and causes localized and systemic disease. The higher adhesion capacity of strains isolated from patients with otitis as compared to strains from sepsis or meningitis patients indicates that binding to the nasopharyngeal mucosa is important in localized but not in invasive infections. The biochemical basis of the pneumococcal binding to epithelial cells has been investigated. Human nasopharyngeal epithelial cells were mixed with pneumococci, and adherence was determined microscopically. Inhibition of adherence with analogues of epithelial cell receptors was tested by preincubation of pneumococci before the addition of the epithelial cells. Competitive inhibition with glycoconjugates, representing receptor structures on the epithelial cell surface, showed receptor function of saccharides containing the disaccharide GlcNAcbeta1 leads to 3Galbeta-.

Disaccharides↗
PubMed1982

Non-contiguous segments of the polyoma genome required in cis for DNA replication.

The boundaries of the origin of polyoma DNA replication have been analyzed using a set of deletion mutants. The majority of these had small deletions, 5 to 30 basepairs in size, which together removed most of the non-translated sequences of the genome. The phenotype of the mutants was characterized by analysis of infectivity, transforming ability and DNA synthesis. All mutants with reduced or abolished infectivity had corresponding defects of viral DNA synthesis. The effect of the deletion was cis-acting, since the replication of the mutants was not stimulated by the presence of wild-type DNA. Deletions causing a reduction of DNA synthesis were found at two sites. The first at the 32 base-pair inverted repeat sequence and the neighbouring A . T tract previously implicated in the initiation of DNA synthesis, and the second close to the late genes. The two sites were separated by at least 60 base-pairs of non-essential DNA. Only one mutant with a deletion at the second site was unable to express early gene functions. The mutants were constructed by linearization, shortening and recircularization of polyoma DNA inserted into the plasmid pBR322. The mutagenesis was directed at restriction endonuclease BglI or PvuII cleavage sites. The BglI-directed mutagenesis was focussed to polyoma DNA by using as a vector a derivative of pBR322 resistant to cleavage by BglI.

Base Sequence↗
PubMed1982

Structure at restriction endonuclease MboI cleavage sites protected by actinomycin D or distamycin A.

Restriction endonuclease MboI cleavage of DNA was inhibited by actinomycin D and distamycin A. The two inhibitors protected different subsets of the 8 cleavage sites in polyoma DNA. The cleavage reactions were analyzed both in the presence of minimal inhibitory concentrations of the compounds and at higher concentrations, allowing cleavage at only 1 site/DNA molecule. The experiments showed that cleavage sites most efficiently protected by actinomycin D had putative inhibitor binding sites at a distance of 1-2 base pairs from the MboI recognition sequence. Distamycin A, in contrast, apparently has to bind immediately adjacent to the MboI recognition sequence to protect from cleavage.

Base Sequence↗
PubMed1982

Sealing of gaps in duplex DNA by T4 DNA ligase.

Single-strand gaps in DNA molecules were found to be a substrate for T4 DNA ligase. Sealing of the gaps was optimal at the same conditions as ligation of blunt-ended DNA molecules. Spermidine at a concentration of 2 mM stimulated the ligation of gaps, as well as the joining of DNA molecules with cohesive and blunt ends. In addition, spermidine reduced the optimal ATP concentration. The ligation of single-stranded gaps was a slow process, reaching a plateau after several hours at 25 degrees C. Approximately 10% of circular duplex plasmid pBR322 DNA molecules with a gap of 1-5 nucleotides could be converted to a covalently closed form. When such molecules were used for transformation of E. coli cells deletion mutants were obtained at a high frequency. The size and position of the gaps and the deletions were equivalent, confirming that T4 DNA ligase was sealing the gaps.

DNA Ligases↗
PubMed1982

Mutagens in larger fungi. I. Forty-eight species screened for mutagenic activity in the Salmonella/microsome assay.

Specimens of large fungi (mushrooms) were screened for mutagenic activity by the Salmonella/microsome assay, with strains TA98, TA2637 and TA100. Our of 48 species tested, 37 exhibited a significant but for the most part weak activity. The activity observed in the presence of S9 mix was typically between 0 and 50% of that without, and in no case was the activity increased in the presence of microsomal enzymes. Six metabolites reported to occur in some of the species included in this investigation were also tested. Significant mutagenic activity was found with isovelleral (5) from Lactarius sp., agaritine (3) from Agaricus bisporus and related sp. and beta-nitraminoalanine (7) from Agaricus silvaticus. Isovelleral may be a major mutagen in some of the sharp-tasting and mutagenic Russulaceae sp. A. bisporus (cultivated specimen) was weakly mutagenic toward all three strains of S. typhimurium, used, and agaritine was weakly active toward TA2637 alone. This implies that this fungus might contain other mutagenic material as well. beta-Nitraminoalanine was not found in the particular collection of A. silvaticus tested here. The mutagenicity observed for the fungus in this work may therefore be due to other metabolites. Even though many species found to be mutagenic are used as food, it seems premature to make specific recommendations about eventual health risks. Further information is needed about the chemistry and toxicology of the active compounds as well as about the effects of various methods used in preparing mushrooms for food.

Animals↗
PubMed1982

Ethidium-bromide-inhibited restriction endonucleases cleave one strand of circular DNA.

We analyzed the effect of ethidium bromide (EtBr) on the cleavage of closed circular pBR322 DNA molecules by six restriction enzymes which make staggered or flush cuts (EcoRI, HindIII, BglI, PstI, HincII, PvuII). EtBr concentrations and reaction temperatures were determined at which DNA molecules with single-strand breaks were the major reaction product of digestion by all the enzymes. However, the amounts of intermediates which could be isolated differed for various enzymes. The results extend previous studies, showing that sequential cleavage of the DNA strands probably is a general property of restriction endonucleases.

DNA Restriction Enzymes↗
PubMed1982

Immunization against the polyoma virus-induced tumor-specific transplantation antigen by early region mutants of the virus.

To investigate the relation between the polyoma tumor-specific transplantation antigen and the virus-coded proteins, mice were immunized by inoculation of a variety of viable polyoma virus mutants and then challenged with polyoma virus-induced tumors. Two classes of early region mutants were used. One class produces a normal small T-antigen and truncated middle and large T-antigens. The second class (hr-t mutants) forms a normal large T-antigen together with N-terminal fragments of small and middle T-antigens. All mutants, transforming as well as nontransforming, induced protection against polyoma virus tumors. However, there were quantitive differences between the mutants. The finding that an hr-t mutant could induce tumor rejection suggests that full-length middle and small T-antigens are not necessary for the induction of this response. Since intact middle T-antigen is the only virus-coded protein known to associate with the plasma membrane, the possibility must be considered that the polyoma virus tumor-specific transplantation antigen consists of cellular components.

Animals↗
PubMed1981

Discontinuous synthesis of both strands at the growing fork during polyoma DNA replication in vitro.

In discontinuous polyoma DNA replication, the synthesis of Okazaki fragments is primed by RNA. During viral DNA synthesis in nuclei isolated from infected cells, 40% of the nascent short DNA fragments had the polarity of the leading strand which, in theory, could have been synthesized by a continuous mechanism. To rule out that the leading strand fragments were generated by degradation of nascent DNA, they were further characterized. DNA fragments from a segment of the genome which replication forks pass in only one direction were strand separated. The sizes of the fragments from both strands were similar, suggesting that one strand was not specifically degraded. Most important, however, the majority of the Okazaki fragments of both strands were linked to RNA at their 5' ends. For identification, the RNA was labeled at the 5' ends by [beta-32P]GTP, internally by [3H]CTP, [3H]GTP, and [3H]UTP, or at the 3' ends by 32P transfer from adjacent [32P]dTMP residues. All three kinds of labeling indicated that an equal proportion of DNA fragments from the two strands was linked to RNA primers.

DNA↗
PubMed1981

Characterization of polyoma mutants with altered middle and large T-antigens.

The viable polyoma mutants dl1013, dl1014, and dl1015 produced shortened middle and large T-antigens. In mouse 3T3 cells, dl1013 and dl1014 grew at normal rates, and dl1015 grew at a reduced rate. dl1015 behaved phenotypically as a double mutant, with deficiencies both in the stimulation of the host cell and the replication of viral DNA. Only the former defect could be complemented by the ts-a mutant, which produced a normal middle T-antigen and a temperature-sensitive large T-antigen. This result suggests that middle T-antigen is involved in the induction of cellular DNA synthesis. Of the three mutants, dl1015 alone failed to transform rat fibroblasts to growth in semisolid medium. This defect could not be complemented by the ts-a mutant. Determination of the base sequences of the mutant DNAs showed that dl1013 and dl1014 had overlapping deletions of 21 and 9 base pairs, respectively, and that the dl1015 deletion of 30 base pairs was contiguous to the other mutations on their 3' sides. Analyses of the mutant t-antigens showed that all three mutants produced shortened middle T-antigens, whereas only dl1015 large T-antigen was detectably reduced in size.

Animals↗