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Biomedical subjects

G S Harris

Publications and source records attributed to G S Harris.

At least 37 records · Page 2Linked to original sources
PubMed1990

Genes required for formation of the apoMoFe protein of Klebsiella pneumoniae nitrogenase in Escherichia coli.

A binary plasmid system was used to produce nitrogenase components in Escherichia coli and subsequently to define a minimum set of nitrogen fixation (nif) genes required for the production of the iron-molybdenum cofactor (FeMoco) reactivatable apomolybdenum-iron (apoMoFe) protein of nitrogenase. The active MoFe protein is an alpha 2 beta 2 tetramer containing two FeMoco clusters and 4 Fe4S4 P centers (for review see, Orme-Johnson, W.H. (1985) Annu. Rev. Biophys. Biophys. Chem. 14, 419-459). The plasmid pVL15, carrying a tac-promoted nifA activator gene, was coharbored in E. coli with the plasmid pGH1 which contained nifHDKTYENXUSVWZMF' derived from the chromosome of the nitrogen fixing bacterium Klebsiella pneumoniae. The apoMoFe protein produced in E. coli by pGH1 + VL15 was identical to the apoprotein in derepressed cells of the nifB- mutant of K. pneumoniae (UN106) in its electrophoretic properties on nondenaturing polyacrylamide gels as well as in its ability to be activated by FeMoco. The constituent peptides migrated identically to those from purified MoFe protein during electrophoresis on denaturing gels. The concentrations of apoMoFe protein produced in nif-transformed strains of E. coli were greater than 50% of the levels of MoFe protein observed in derepressed wild-type K. pneumoniae. Systematic deletion of individual nif genes carried by pGH1 has established the requirements for the maximal production of the FeMoco-reactivatable apoMoFe protein to be the following gene products, NifHDKTYUSWZM+A. It appears that several of the genes (nifT, Y, U, W, and Z) are only required for maximal production of the apoMoFe protein, while others (nifH, D, K, and S) are absolutely required for synthesis of this protein in E. coli. One curious result is that the nifH gene product, the peptide of the Fe protein, but not active Fe protein itself, is required for formation of the apoMoFe protein. This suggests the possibility of a ternary complex of the NifH, D, and K peptides as the substrate for the processing to form the apoMoFe protein. We also find that nifM, the gene which processes the nifH protein into Fe protein (Howard, K.S., McLean, P.A., Hansen, F. B., Lemley, P.V., Kobla, K.S. & Orme-Johnson, W.H. (1986) J. Biol. Chem. 261, 772-778) can, under certain circumstances, partially replace other processing genes (i.e. nifTYU and/or WZ) although it is not essential for apoMoFe protein formation. It also appears that nifS and nifU, reported to play a role in Fe protein production in Azotobacter vinelandii, play no such role in K. pneumoniae, although these genes are involved in apoMoFe formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1989

Characterization of alpha and beta tubulin genes in the dimorphic fungus Histoplasma capsulatum.

Evidence from our laboratory indicates that microtubules are involved in the differentiation of the dimorphic, pathogenic fungus Histoplasma capsulatum; therefore, we cloned the tubulin genes from a virulent strain of the organism. We report that the H. capsulatum genome contains a single alpha (TUB1) and a single beta (TUB2) tubulin gene rather than the more typical multigene family which is common in even the simplest eukaryotes. Sequence data from these genes reveal a high degree of nucleotide and protein sequence conservation relative to tubulins from other species. The coding regions of TUB1 and TUB2 contain five and eight intervening sequences, respectively. Field inversion gel electrophoresis of H. capsulatum chromosome-sized DNA fragments indicates that the TUB1 and TUB2 genes are unlinked. Potential regulatory elements common to both genes have been identified in the 5' promoter regions. These elements may direct the coordinate expression of TUB1 and TUB2 during differentiation. The cloning and characterization of alpha and beta tubulin genes from H. capsulatum provides the first description of gene structure in this widely distributed pathogenic fungus. Isolation of the tubulin genes will facilitate future studies of tubulin gene expression during the dimorphic phase transitions and clarify the role of microtubules in the differentiation process.

Amino Acid Sequence↗
PubMed1989

Expression of alpha- and beta-tubulin genes during dimorphic-phase transitions of Histoplasma capsulatum.

Recent investigations have confirmed the presence of one alpha-tubulin gene (TUB1) and one beta-tubulin gene (TUB2) in the dimorphic fungus Histoplasma capsulatum. In the present study, Northern blot (RNA blot) analyses revealed multiple alpha-tubulin transcripts and a single beta-tubulin transcript in the yeast and mycelial phases of the high-virulence 217B strain and low-virulence Downs strain. S1 nuclease protection assays demonstrated one initiation start site and two major stop sites for the TUB1 transcripts, suggesting that variations in 3' processing generate the alpha-tubulin messages of 2.5 and 2.0 kilobases. Dot blot hybridization experiments indicated that tubulin gene expression is developmentally regulated during the dimorphic phase transitions. alpha- and beta-tubulin mRNAs increased six- to eightfold during the yeast-to-mycelium conversion and decreased two- to threefold during the reverse transition. These changes in tubulin mRNA content coincided with major morphological events associated with H. capsulatum development. Western blots (immunoblots) of H. capsulatum yeast-specific proteins resolved by two-dimensional gel electrophoresis demonstrated a single alpha- and a single beta-tubulin isoform. Multiple tubulin polypeptides expressed in mycelia are probably products of posttranslational modifications.

Endonucleases↗
PubMed1986

Pseudomonas aeruginosa and cystic fibrosis: unusual bacterial adaptation and pathogenesis.

Pseudomonas aeruginosa is an adaptable, saprophytic bacterium with the potential to cause a variety of opportunistic infections in compromised hosts. In patients with cystic fibrosis, chronic pulmonary colonization with mucoid alginate-producing mutants of P. aeruginosa is a major cause of morbidity and mortality and is an interesting example of microbial adaptation and host-bacterium interaction.

Adaptation, Physiological↗
PubMed1985

An examination of the prepatent period and the absence of a crowding effect in Angiostrongylus cantonensis in laboratory rats.

The effects of the size of the infective inoculum on the prepatent period and the effect of crowding on body volume were examined in populations of Angiostrongylus cantonensis (Metastrongyloidea: Angiostrongylidae) in the laboratory rat. Groups of five rats were infected with 5, 10, 20 and 40 L3 of A. cantonensis, respectively. The prepatent period was determined by examination of faeces using a modified Baermann technique. The prepatent period ranged from 37 to 45 days and was best described by a negative logarithmic curve (y = 51.21 + x-3.838). Based on developmental data in the literature, it is suggested that 37 days represents the minimum prepatent period for A. cantonensis in this host. Worm population showed a significant, positive increase with inoculum size, yet there was no relationship between worm volume and population size in females and a slight, but significant, increase in worm volume and population size in males from rats necropsied 76-84 days post-infection. It is concluded that crowding is likely to have little effect on worm size in rats naturally infected with A. cantonensis.

Angiostrongylus↗
PubMed1984

Assessment of anti-streptokinase antibody levels in human sera using a microradioimmunoassay procedure.

A high capacity, quantitative radioimmunoassay procedure has been developed to measure IgG antibodies to streptokinase (SK) in human serum. Results showed that the use of low concentrations of 125I-SK (100 ng/ml) and ambient temperature incubation conditions minimised degradation of the target labelled antigen and afforded antibody binding values which could be confidently related to the native intact SK protein. SK-complexed to plasminogen was also shown to retain the equivalent antigenic activity of native SK. Comparison of the absolute anti-SK levels with streptokinase resistance titres demonstrated that the two measurements of antibody correlated statistically but afforded quantitatively poor agreements. A survey of IgG levels to SK in sera from 93 normal healthy volunteers showed that all individuals displayed readily measurable anti-SK antibodies, with some 80% having IgG concentration capable of binding in excess of 1 microgram SK per ml serum.

Antibodies↗
PubMed1984

Comparison of the hypotensive effects of streptokinase-(human) plasmin activator complex and BRL 26921 (p-anisoylated streptokinase-plasminogen activator complex) in the dog after high dose, bolus administration.

In view of current interest in the possibility of rapid, high-dose administration of thrombolytic agents by the intravenous route in patients with coronary thrombosis (AMI), a study of this technique was carried out in the dog. Streptokinase-(human) plasmin activator complex (SK-Pm) and BRL 26921 (p-anisoylated streptokinase-(human) plasminogen activator complex) were each given at equivalent doses (28,500 IU/kg and 800 micrograms/kg respectively) to groups of beagle dogs by rapid injection over 10 sec and their effects on blood pressure, plasmin formation and kallikrein production were compared over the next 3h. SK-Pm produced, within 1-3 min, a pronounced hypotensive effect that was kinetically related to a rapid and steep rise in systemic plasmin and kallikrein concentrations. BRL 26921 had no hypotensive effect, the rise in plasmin production was slower and the rate and extent of kallikrein formation was significantly less than in the SK-Pm group.

Animals↗
PubMed1984

Choroidal osteomas.

Two cases of choroidal osteoma (one bilateral) are reported, bringing the total number of cases in the English-language literature to 18; an additional 7 cases are known to the authors. This tumour, first described in 1978, arises in the inner third of the juxtapapillary choroid and consists of mature bone; it is likely an osseous choristoma. It transmits light in an unusual manner, small lacunae glowing with sclerotic scatter. If the bony plaque is peripheral its solid nature can be identified with scleral depression. Computerized tomography readily demonstrates the calcification and the pattern of bone density.

Adult↗
PubMed1982

Management of infective endophthalmitis by pars plana vitrectomy.

Endophthalmitis is an ocular disaster that frequently leads to blindness. With the advent of vitrectomy and the opportunity for intraocular injection of antibiotics more of the eyes can be salvaged. In 11 patients the infection was controlled by vitrectomy. All had dramatic relief of pain, and eight showed an improvement in visual acuity. Pathogens were cultured from the aqueous or the vitreous, or both, of 64%, and from the conjunctival swabs of the remainder.

Adult↗
PubMed1981

A randomized prospective study of the use-effectiveness of two methods of natural family planning.

The final results of a prospective comparative study of two methods of natural family planning indicate a significant difference in the 12 month net cumulative pregnancy rates between the ovulation and symptothermal methods. These differences are on the order of two to one in favor of the symptothermal method. Pearl pregnancy rates confirm similar differentials between the two methods. Dropout rates for both methods were high. Lack of interest or dissatisfaction with the method was the major reason for dropout training while pregnancy or desire for pregnancy were the major reasons for dropout during the formal phase of the study.

Adult↗
PubMed1981

Subinternal limiting lamina hemorrhages associated with sudden vascular pressure rise: yellow preretinal hemorrhages.

A group of patients with subinternal limiting lamina hemorrhages associated with the Valsalva maneuver have been described. A majority of the patients have shown a striking yellowish coloration to the globular preretinal lesions during their evolution. This unique coloration is probably due to the accumulation of bilirubin during hemoglobin disintegration. Visual prognosis is usually excellent and no retinal or vascular abnormalities have been found after the hemorrhage disappears. The unusual fundus picture presented by this lesion may pose diagnostic problems if the patient is initially seen when this yellow mass is present.

Adult↗
PubMed1980

Yellow coloration of preretinal (subhyaloid) hemorrhages associated with a sudden increase in intravascular pressure.

Among seven patients with preretinal (subhyaloid) hemorrhages associated with the Valsalva maneuver a striking yellow coloration of the globular lesions was noted during their evolution in five. The coloration was probably due to the accumulation of bilirubin during hemoglobin disintegration. The visual prognosis in such cases is usually excellent unless unless the hemorrhage is massive, and no retinal or vascular abnormalities have been found after the hemorrhage has disappeared. The unusual appearance of the fundus may pose diagnostic problems if the patient is initially seen when the mass is yellow.

Adult↗
PubMed1979

A randomized prospective study of the use-effectiveness of two methods of natural family planning: an interim report.

Data accumulated to date from the Los Angeles study indicate that the total termination rate for 12 months from the beginning of the training period and from formal entry into the study was high for the ovulation method (OM), and symptothermal method (STM). Voluntary withdrawal was the highest single reason for termination in both methods. The 12 month voluntary withdrawal rate, measured from formal entry into the study, was significantly higher for OM users. Pregnancy rates measured from both the beginning of training and formal entry into the study were significantly higher for OM users than for STM users. Complete analysis of the data collected during the study is currently in progress. It is anticipated that some of the causes for the differences in pregnancy rates and withdrawal rates between the two methods can be identified.

Adult↗
PubMed1977

The prophylactic treatment of retrolental fibroplasia.

10 premature infants with stage 3 retinopathy of prematurity have had photocoagulation and/or cryocoagulation therapy to one eye and have been followed for a period of 1-6 years. Although the long-term results of this therapy are not known, particularly in the prevention of retinal detachment, early observations suggest that treatment is neither harmful nor particularly beneficial. Macular dragging does not seem to be influenced by treatment. The refractive error, as one would expect, does not appear to be altered by this form of therapy. Marked amelioration of the vascular dilatation and tortuosity at the posterior pole is apparent shortly after treatment. It is stressed that this is a trial project and until more definite beneficial results are obtained, treatment of stage 3 retinopathy should be deferred. Retinal detachments (stage 4) may be quite amenable to a buckling procedure.

Child↗
PubMed1976

Visual field changes in branch retinal 'vein' occlusion.

The visual field defects in 20 consecutive patients who had branch retinal "vein" occlusions included arcuate nerve fiber bundle scotomas, central scotomas, paracentral scotomas, and segmental peripheral constriction. The role of retinal arteriolar insufficiency in the production of these field defects is discussed. The available evidence suggests that the term "branch retinal vascular occlusion" is a preferable term to describe such clinical findings.

Adult↗
PubMed1976

Maculopathy of sex-linked juvenile retinoschisis.

Observations in 14 eyes in 7 patients with sex-linked juvenile retinoschisis over a 4 to 8 year period show that the maculopathy tends to progress through a series of stages (Figs. 14, 15, 16) which are associated with increasing impairment in visual acuity. Electrical changes confirm the pathological state of the macula but suggest a pan-retinal disease. Desite the clinical appearance, the extramacular retina seems to be significantly affected. The basic pathological condition may be in the Muller cells. We have been unable to distinguish carriers from normal individuals.

Adolescent↗
PubMed1976

Coats' disease: A study of cholesterol transport in the eye.

An attempt to establish an animal model (rabbit) to study deposition and transport of cholesterol in the eye has been described. Interesting findings include the deposition of cholesterol in the choroid, sclera, and anterior cornea of rabbits fed on a high cholesterol diet. Injected intravitreal cholesterol is seen to leave through the retina, optic nerve head, and the trabecular meshwork. This process appears to be very slow. During the 4 months of observation the yellow preretinal deposits decreased little in size. Only 1 rabbit showed a picture typical of Coats' disease with serous detachment of the retina, subretinal lipoidal deposits and preretinal neovascularization. Although these results are preliminary, they suggest that fatty materials may pass through the retina into the subretinal space from the vitreous and might explain the pathogenesis of Coats' disease in the human.

Animals↗