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Biomedical subjects

G R Smith

Publications and source records attributed to G R Smith.

At least 253 records · Page 14Linked to original sources
PubMed1984

Recombinational hotspot activity of Chi-like sequences.

Chi sites, consisting of the nucleotide octamer 5' G-C-T-G-G-T-G-G 3', stimulate coliphage lambda recombination mediated by the Escherichia coli RecBC recombination pathway. In a sensitive genetic assay using phage lambda crosses, three of four Chi-like sequences tested, namely 5' A-C-T-G-G-T-G-G 3', 5' G-T-T-G-G-T-G-G 3' and 5' G-C-T-A-G-T-G-G 3', had about 6%, 11% and 38% of full Chi activity, respectively. We conclude that certain Chi-like sequences manifest a spectrum of recombinational hotspot activities and may account for RecBC-mediated generalized recombination of lambda lacking Chi sites.

Alleles↗
PubMed1984

The pathogenic properties of Fusobacterium and Bacteroides species from wallabies and other sources.

Intracerebral inoculation was more effective than intraperitoneal, intravenous or subcutaneous inoculation as a means of producing lethal infections with Fusobacterium necrophorum in mice. Strains varied in virulence but, of five examined, two had LD50 values as low as ca. 8000 and 14000 viable organisms. Profuse bacterial multiplication in the brain was demonstrated. Intravenous vaccination with a single large dose of heat-killed whole culture or washed bacterial cells failed to protect against intracerebral challenge. Intracerebral injection of other fusobacteria (F. nucleatum, F. varium and F. necrogenes) and of 22 strains belonging to 10 Bacteroides spp. was without apparent effect on mice, except for a slight transient illness in some animals given B. fragilis. This organism (five strains) differed from the other Bacteroides spp. tested, which included eight strains belonging to the fragilis group, in being eliminated more slowly from the mouse brain--a point that may be relevant to the special pathogenicity of B. fragilis in endogenous infections in man. There was no evidence that B. fragilis multiplied in the brain or that intravenous vaccination with a large dose of heat-killed homologous culture affected the rate at which it was eliminated.

Animals↗
PubMed1984

A study of F38-type and related mycoplasmas by mycoplasmaemia and cross-immunization tests in mice.

In vivo methods were used to study the F38-type mycoplasma in parallel with related mycoplasmas. Three of five strains of 'bovine serogroup 7' with an unknown history of subculture produced mycoplasmaemia in mice inoculated intraperitoneally. A strain of 'bovine serogroup L' also produced mycoplasmaemia, but no evidence of similar ability could be found for single strains of Mycoplasma capricolum, M. equigenitalium and M. primatum, or for two strains of the F38-type mycoplasma. In cross-immunization tests a bovine serogroup 7 strain (NCTC 10133) and a strain ('Blenheim') of the SC (small colony) type of M. mycoides subsp. mycoides were used for the purpose of challenge. Cross-protection was described as 'complete' or 'partial', depending on whether it was as great as, or less than, that produced by homologous vaccine. Although strain NCTC 10133 protected strongly, possibly completely, against Blenheim, and Blenheim gave partial protection against NCTC 10133, challenge with NCTC 10133 and Blenheim gave strikingly different results. Thus (1) F38-type strains, M equigenitalium and M. primatum all gave partial cross-protection against NCTC 10133 but not against Blenheim, (2) NCTC 10133, unlike Blenheim, was seldom susceptible to partial cross-protection by LC (large colony) strains of M. mycoides subsp. mycoides, and (3) three SC strains - which would have protected completely against Blenheim - protected only partially against NCTC 10133. NCTC 10133 and Blenheim were similar, however, in that M. capricolum and M. mycoides subsp. capri failed to cross-protect against them both.

Animals↗
PubMed1984

A new class of Escherichia coli recBC mutants: implications for the role of RecBC enzyme in homologous recombination.

Mutants of Escherichia coli sensitive to phage T4 gene 2 mutants were obtained following ethyl methanesulfonate mutagenesis. By mapping and complementation analysis, the mutations in each of the six mutants are in recB and recC. By both in vivo and in vitro analyses, the nuclease activity of RecBC enzyme is undetectable in these mutants. However, by several other criteria, such as proficiency in recombination, relative resistance to UV radiation, and viability of the cells in the culture, these mutants are almost identical to their recBC+ parent. The properties of these mutants indicate that the ATP-dependent double-stranded DNA exonuclease activity of RecBC enzyme is not required for recombination. Chi recombinational hotspots, which stimulate recombination by the RecBC pathway, have no detectable activity in the mutants. This result suggests that the nuclease activity of RecBC enzyme is required for Chi activity and is consistent with the hypothesis that Chi stimulates recombination by directing RecBC enzyme to cut DNA at or near Chi.

Crosses, Genetic↗
PubMed1984

Unusual alleles of recB and recC stimulate excision of inverted repeat transposons Tn10 and Tn5.

Precise and nearly precise excision of transposon Tn10 occur by host-mediated processes unrelated to transposition. Both types of excision involve interactions between short (9 or 24 base-pair) direct repeat sequences at or near the termini of the transposon and are stimulated by the large (1,329-base-pair) inverted repeats that form the ends of Tn10. We describe here three mutations of Escherichia coli K-12, designated texA, that enhance excision of Tn10 and of the structurally analogous transposon Tn5. Genetic mapping and complementation analysis show that these mutations are unusual alleles of the recB and recC genes that alter but do not abolish RecBC function. As Tn10 excision normally does not depend on RecA or RecBC functions, texA mutations appear to provide another pathway for excision that depends on altered RecBC function; for one texA allele, excision has become dependent on RecA function as well. The available evidence suggests that texA mutations alter the stimulatory interaction between the inverted repeats of Tn10.

Alleles↗
PubMed1984

Thirteen cases of botulism in horses fed big bale silage.

An outbreak of pharyngeal and limb paresis involving four horses and nine ponies in the south east of England is described. Nine of the animals died or were destroyed on humane grounds. The clinical features suggested a diagnosis of botulism and mouse innoculation tests confirmed the presence of type B toxin in the serum of one case. All animals were fed big bale silage. It is describe how, in plastic wrapped silage manufacture, conditions of fermentation may be inadequate to prevent the growth of Clostridium botulism. Examination of a sample of silage fed to the affected horses suggested that this was probably the source of the toxin.

Animal Feed↗
PubMed1984

Escherichia coli recBC deletion mutants.

Mutants of Escherichia coli with deletions of the recB and recC genes were obtained by two methods using transposable DNA elements. The phenotypes of these mutants are similar to those of mutants with recBC point mutations. These results indicate that the RecBC gene products, exonuclease V, is not essential for the growth of E. coli but is important for DNA repair and recombination.

Chromosome Deletion↗
PubMed1984

An analysis of Mycoplasma mycoides by in vivo methods.

Fresh isolates of the small colony (SC) type of Mycoplasma mycoides subsp. mycoides readily produced mycoplasmaemia in mice inoculated i.p. The mycoplasmaemic capability of large colony (LC) strains was much less by comparison. Cross-immunization and -hyperimmunization tests in mice were made by injecting vaccines i.v., challenging i.p., and assessing the results on the presence or absence of mycoplasmaemia at daily intervals thereafter, as demonstrated by tail-blood culture in a selective medium. In terms of mouse-protective antigens, the SC and LC types were related but not identical. SC strains, unlike LC strains, were homogeneous. The SC and LC types differed from M. mycoides subsp. capri but were nonetheless related to it, the former less closely than the latter. Cross-immunization by M. mycoides subsp. mycoides (SC and LC types) against M. mycoides subsp. capri was often, but not always, unidirectional.

Animals↗
PubMed1984

Aetiological agents of necrobacillosis in captive wallabies.

In a series of 27 wallabies (Macropus rufogriseus) with necrobacillosis, 14 animals were affected in the face, nine in the leg and six in the internal organs, two being affected in more than one site. Fusobacterium necrophorum was the predominating organism, occurring in 69 per cent of lesions, usually in heavy and occasionally in pure culture. Bacteroides species (six in all), often in considerable numbers, were found in 48 per cent of lesions, and F nucleatum in 14 per cent. Aerobes or facultative anaerobes, usually in small numbers, were present in 59 per cent of lesions. The organisms isolated often varied considerably from one part of the lesion to another.

Animals↗
PubMed1983

Nucleotide sequence of the lysozyme gene of bacteriophage T4. Analysis of mutations involving repeated sequences.

The nucleotide sequence of the lysozyme (e) gene of bacteriophage T4 and approximately 130 additional nucleotides on each side has been determined. The 5'-end of the gene for internal protein III appears to be located about 70 base-pairs from the 3'-end of the lysozyme gene. Nucleotide sequence analysis of mutant e genes confirmed that three identified hotspots of frameshift mutations are runs of five A nucleotides in the wild-type gene. The endpoints of two deletions are direct repeats of eight base-pairs in the wild-type gene. Two frameshift mutations with high reversion frequencies are duplications of five or seven base-pairs. The cloning and nucleotide sequence determination of the lysozyme gene will facilitate further study of the molecular biology of T4 lysozyme.

Base Sequence↗