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At least 541 records · Page 30Linked to original sources
PubMed1969

Polyoma virus gene activity during lytic infection and in transformed animal cells.

Randomly labeled RNA's from animal cells either productively infected or transformed by polyoma virus were used to measure virus DNA transcription. During lytic infection, 50 percent of polyoma virus DNA was expressed. In two different polyoma-transformed hamster cell lines, the same 20 percent of the virus genome was transcribed. About 10 percent of polyoma DNA was expressed in the one mouse transformed cell line examined.

Animals↗
PubMed1969

Multiplicity reactivation as a test for recombination function.

Multiplicity reactivation of bacteriophage inactivated by ultraviolet light is dependent on the recombination function of either the host bacterial cell or the infecting bacteriophage. Absence of both recombination systems leads to a loss of multiplicity reactivation.

Coliphages↗
PubMed1969

Self-assembly of Q-beta and MS2 phage particles: possible function of initiation complexes.

Four kinds of particles were reconstituted with RNA and protein from the genetically unrelated bacteriophages Qbeta and MS2, namely, two homologous and two heterologous, with respect to RNA and protein. However, once Qbeta RNA (or MS2 RNA) reacted with a few molecules of either Qbeta or MS2 protein to form a nucleoprotein complex (initiation complex), it formed a phagelike particle only with subsequent addition of the same protein.

Centrifugation, Density Gradient↗
PubMed1970

Visualization of bacterial genes in action.

The morphology of active structural and putative ribosomal RNA genes was observed by electron microscopy after lysis of fragile Escherichia coli cells. Conclusions drawn are: most of the chromosome is not genetically active at any one instant; translation is completely coupled with transcription; the 16S and 23S ribosomal RNA cistrons occur in tandem, in regions which are widely spaced on the chromosome.

Chromosomes, Bacterial↗
PubMed1980

Variation in susceptibility patterns of species within the Bacteroides fragilis group.

Minimal inhibitory concentrations of eight antibiotics were determined for 159 clinical isolates of members of the Bacteroides fragilis group using the National Committee for Clinical Laboratory Standards proposed agar dilution reference method. Isolates were identified by standard techniques with deoxyribonucleic acid homolog confirmation. These closely related species demonstrated differences in susceptibility to commonly used drugs.

Anti-Bacterial Agents↗
PubMed1969

Some properties of the beta-lactamase genes in Staphylococcus epidermidis.

Eighty-three per cent of 200 different freshly isolated cultures of Staphylococcus epidermidis produced beta lactamase. Growth in the presence of acridine orange or ethidium bromide or growth at 44 C resulted in a high frequency of loss of the beta lactamase genes in some strains of S. epidermidis. The relationship between beta-lactamase production and resistance to mercuric, cadmium and arsenate ions differed from that observed in Staphylococcus aureus. It is postulated that the genes for beta lactamase in certain strains of S. epidermidis are on a plasmid.

Acridines↗
PubMed1970

In vitro and in vivo studies of streptomycin-dependent cholera vibrios.

Streptomycin-dependent cholera vibrio strains were derived from Inaba, Ogawa, and NAG vibrios by the method of Mel. These phenotypes grew more slowly and attacked fermentable substances after a longer period of time than the streptomycin-sensitive parent strains. Rabbits injected with streptomycin-sensitive strains and their streptomycin-dependent forms showed homologous agglutinin production. Patas monkeys fed with 10(9) streptomycin-dependent strains shed them for 1 to 2 days without ill effect, whereas the same number of streptomycin-independent organisms caused disease. The possibility of the application of multiple doses of streptomycin-dependent organisms in oral immunization against cholera was considered.

Agglutination Tests↗
PubMed1970

Production of nucleic acid-related substances by fermentation processes. 33. Accumulation of inosine by a mutant of Brevibacterium ammoniagenes.

Inosine-producing cultures were found among mutants resistant to 6-mercaptoguanine (6MG) derived from a 5'-inosinic acid (IMP)-producing strain, KY 13102, of Brevibacterium ammoniagenes. Inosine-producing ability was very frequent among the mutants resistant to a low concentration (10 to 50 mug/ml) of 6MG. The accumulation of inosine by strain KY 13714 was stimulated by a low concentration of adenine (25 mg/liter) but was depressed by high levels of adenine. The accumulation by strain KY 13714 was not inhibited by manganese ion but instead was stimulated by its excess, in contrast to IMP accumulation by KY 13102. Addition of hypoxanthine at an early stage of cultivation accelerated inosine accumulation. Furthermore, on addition of hypoxanthine and of a surface-activating agent after 48 hr of cultivation, the simultaneous accumulation of IMP and inosine was observed. A 9.3-mg amount of inosine per ml accumulated after 4 days of cultivation at 30 C. The inosine-producing mutant did not differ from the IMP-producing strain either in 5' purine nucleotide degradation or in IMP formation from hypoxanthine. However, it was found to be completely devoid of purine nucleoside-degrading activity. The conversion of IMP accumulation to inosine can be explained by the lack of nucleosidedegrading activity. The relationship between deficiency of nucleoside-degrading activity and resistance to low levels of 6MG is discussed, and a new mechanism for 6MG resistance is presented.

Adenine↗
PubMed1970

Probability distribution of drug-resistant mutants in unselected populations of Mycobacterium tuberculosis.

The fluctuation test shows that Mycobacterium tuberculosis mutates to resistance to isoniazid, streptomycin, ethambutol and rifampin spontaneously and at random. The average mutation rates for the drugs, in the same order, were calculated to be 2.56 x 10(-8), 2.95 x 10(-8), 10(-7), and 2.25 x 10(-10) mutation per bacterium per generation. The relatively high mutation rate to ethambutol resistance and the low mutation rate to rifampin resistance were confirmed by analyzing the increase in the proportion of mutants with time in a growing population of the tubercle bacilli. The highest proportions of mutants to be expected in unselected populations of the tubercle bacilli were calculated from the results of fluctuation tests.

Culture Media↗
PubMed1972

Factors affecting virulence of Shigella flexneri: strain with relaxed control of ribonucleic acid synthesis.

An Escherichia coli-Shigella flexneri hybrid strain which produces an abortive, nonfatal experimental dysentery has inherited relaxed control of ribonucleic acid synthesis from its E. coli parent. This property, coupled with a partial methionine requirement, has been used to explain its long lag phase in vitro, relative to its Shigella parent. It was suggested that such characteristics may contribute to the hybrid's poor survival in the gut resulting in the abortive infection.

Alleles↗
PubMed1972

Genetic control of host responses to endotoxin.

Two pathophysiological effects of endotoxin in mice have been shown to be under the major influence of polygenic inheritance. The first, endotoxemia, was measured by LD(50) assays on hybrids and backcross hybrids of the resistant C(3)H/HeJ and the susceptible A/HJe strains. The LD(50) values of the F1 hybrids and the backcross hybrids were intermediate between the respective parental types. The second effect, the intraperitoneal extravascular leukocyte response to small doses of endotoxin, also was found to follow characteristic patterns of polygenic inheritance. As estimated from an analysis of the variance of mice of the F1 and F2 generations, the degree of genetic determination is approximately 54% for the neutrophil response and 82% for the monuclear response.

Animals↗
PubMed1974

Role of typhoid antigens in protection and pathogenicity for mice.

Swiss white mice immunized with acetone-killed vaccines prepared from strains of Salmonella typhosa, S. typhimurium, and mouse-virulent S. typhimurium hybrids which had acquired, by conjugal genetic transfer, the S. typhosa antigens 9, Vi, and d were challenged with the S. typhimurium hybrids and with the S. typhimurium parent strain. The results of these experiments suggested that the Salmonella somatic antigens were important in conferring protection against death in this system. The S. typhosa Vi antigen did not appear to play any significant role in this protection. The S. typhimurium hybrids employed in these studies did not show any loss of mouse virulence as the consequence of acquisition of various combinations of the S. typhosa somatic, flagella, or Vi antigens, nor did S. typhosa hybrids which had acquired the somatic antigen of S. typhimurium show any increase in mouse virulence.

Animals↗
PubMed1969

Resistance of Salmonella typhimurium mutants to galactose death.

A class of galactose-resistant mutants has been derived from strains of Salmonella typhimurium which are defective in uridine diphosphoglucose-4-epimerase. Resistant strains are phenotypically similar to parent organisms but do not lyse in the presence of galactose. Low levels of functional epimerase can be detected in induced cells grown at 20 C but not at 37 C, and acid is not produced from galactose. Sufficient galactose is synthesized at reduced temperatures to fabricate smooth lipopolysaccharide and acceptor sites for phage P22 from galactose-deficient media. The leaky nature of these mutants may account for resistance to galactose death by maintaining galactose metabolites at a subcritical level. Glucose protects sensitive strains by control of levels of toxic metabolites by catabolite repression.

Bacteriolysis↗
PubMed1970

Reassociation of deoxyribonucleic acids from Actinoplanes and other actinomycetes.

The ability of deoxyribonucleic acid (DNA) isolated from a number of actinomycetes to reassociate with reference DNA from Actinoplanes philippinensis or Streptomyces venezuelae has been measured. All of the DNA preparations except for those from Nocardia erythropolis and Thermomonospora viridis contained 70 to 73 moles per cent guanine and cytosine. DNA from two species of Actinoplanes, two species of Dactylosporangium, and Ampullariella digitata formed extensive thermally stable duplexes with the Actinoplanes philippinensis reference. DNA from streptomycetes formed duplexes with the A. philippinensis reference, but these duplexes possessed low thermal stability. DNA from N. erythropolis and T. viridis did not bind significant amounts of this reference DNA. Only DNA from Streptomyces albus, Streptoverticillium baldaccii, and Microellobosporia flavea appreciably bound the Streptomyces venezuelae reference. Our results separate the actinomycetes forming sporangia into two groups: the first group contained Actinoplanes, Dactylosporangium, and Ampullariella; the second group contained Planomonospora, Spirillospora, and Streptosporangium.

Actinomycetales↗
PubMed1970

Specific labeling and physical characterization of R-factor deoxyribonucleic acid in Escherichia coli.

The molecular nature of R-factor deoxyribonucleic acid (DNA) was examined in Escherichia coli by using a method for the specific labeling of the derepressed R factor, R1, in a female cell after conjugation. Sixty minutes after mating, the R factor was isolated as a single molecule with a molecular weight of 65 x 10(6) daltons. This single molecular species sedimented as either a covalently closed molecule or a "nicked" circle. When the single R-factor component was centrifuged in a CsCl density gradient, only a single homogeneous species with a buoyant density of 1.711 g/cm(3) was observed. R-factor DNA was also isolated directly from exponentially growing cells of E. coli as a covalently closed single molecular species comprising about 1% of the total cellular DNA. Previous studies in Proteus show that R1 factor DNA components of buoyant density 1.709, 1.711, and 1.716 g/cm(3) can be identified as distinct replicons. It is suggested that the single molecule of R1 observed in E. coli is most simply explained as a composite structure resulting from a recombinational assemblage of a 1.709 and 1.716 g/cm(3) replicon.

Centrifugation, Density Gradient↗
PubMed1970

Conservation and transfer of Escherichia coli genetic segments by partial diploid Hfr strains of Salmonella typhosa.

Heterozygous, partial diploid hybrids were obtained in a Salmonella typhosa Hfr strain by using it as the recipient in a mating with the Escherichia coli Hfr donor WR2004 (O...proA...leu). Three of these S. typhosa Hfr hybrids were observed to mobilize and transfer the diploid E. coli genes, at high frequencies, to an E. coli recipient. The gradient of transfer frequencies of E. coli markers from these S. typhosa Hfr hybrids was similar to that observed with E. coli Hfr WR2004, from which they were derived. Interrupted matings with one of these S. typhosa Hfr hybrids, designated WR4272, showed the entry times for the proA, thr(-)leu, and argB E. coli diploid markers to be identical to the times obtained for these markers with E. coli Hfr WR2004. Also, the pattern of unselected inheritance of the diploid E. coli markers of S. typhosa Hfr hybrid WR4272 was similar to that observed with the chromosomal markers of E. coli Hfr WR2004. It was concluded that S. typhosa Hfr hybrid WR4272 contains, in addition to its Salmonella genome, a physically continuous E. coli chromosomal segment which is genetically complete from proA to at least the strA locus. The two other S. typhosa Hfr hybrids, on the basis of transmission frequency gradients, appeared to contain a continuous E. coli diploid segment complete from proA through the fuc locus. Other classes of S. typhosa Hfr hybrids, derived from mating with E. coli Hfr WR2010 (O...tna...xyl), were also observed to transfer E. coli genes at high frequency.

Chromosome Mapping↗