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A Varma

Publications and source records attributed to A Varma.

17 recordsLinked to original sources
PubMed1992

Molecular and genetic analysis of URA5 transformants of Cryptococcus neoformans.

Cryptococcus neoformans var. neoformans ura5 mutants were transformed with linearized or circular plasmids containing the C. neoformans orotidine monophosphate pyrophosphorylase gene. Following electroporation, randomly isolated transformants were analyzed for the mitotic and meiotic stability of uracil prototrophy. All stable transformants tested showed nonspecific ectopic integration. Uracil prototrophy in these transformants was stable through meiosis. Some of the stable transformants showed integration of both URA5 and vector sequences, while others lacked any vector sequences. Unstable transformants exhibited the presence of an autonomously replicating plasmid which had undergone significant sequence rearrangement. The autonomously replicating plasmid in the transformants was observed to be the same size or smaller than the transforming plasmid, was maintained in a linear form, and had acquired a genomic sequence(s) with homology to a sequence(s) on all the chromosomes. The conservation of a 300-bp sequence at the 5' end of the URA5 gene was observed in all the rearranged plasmids. These results suggest mechanisms of plasmid maintenance in C. neoformans that are different from those reported for other yeasts. The ura5 mutant was significantly less virulent than the wild type. The transformants did not recover virulence regardless of prototrophic stability.

Chromosome Mapping↗
PubMed1992

DNA probe for strain typing of Cryptococcus neoformans.

A 7-kb linear plasmid, harbored by a URA5 transformant, hybridized to all the chromosomes of Cryptococcus neoformans separated by contour-clamped homogeneous electric field electrophoresis. Its linear maintenance was determined to have been facilitated by the presence of telomere-like sequences at its free ends. Hybridization of this plasmid to AccI-digested genomic DNAs of 26 C. neoformans strains generated 21 unique DNA fingerprints. The DNA fingerprints of isolates within the same serotype were more similar to one another than to those from different serotypes. An acapsular clinical isolate, strain 602, widely used in immunological studies and previously thought to be in serotype D, showed DNA fingerprints typical of serotype A isolates. Isogenic strains of C. neoformans exhibited DNA fingerprints that were identical to one another. The DNA fingerprints were stable and reproducible in spite of repeated transfers in the laboratory on either complex (1% yeast extract, 2% Bacto Peptone, 2% glucose) or minimal (yeast nitrogen base) medium. The DNA fingerprints of isolates recovered from primary blood and cerebrospinal fluid cultures of patients for whom AIDS had been diagnosed showed that the original infection in each of these patients contained a homogeneous population of C. neoformans. The DNA fingerprints of isolates recovered from different tissues of infected mice and from patients undergoing different drug therapy regimens were also found to be very stable.

AIDS-Related Opportunistic Infections↗
PubMed1992

Selection of ura5 and ura3 mutants from the two varieties of Cryptococcus neoformans on 5-fluoroorotic acid medium.

Spontaneous mutants requiring uracil were isolated from both varieties of Cryptococcus neoformans by plating on 5-fluoroorotic acid (5-FOA) medium. Of the 36 strains tested (18 var. neoformans and 18 var. gattii), 24 (12 of each variety) generated 5-FOA-resistant cells requiring uracil for growth. Six of the 12 C. neoformans var. gattii strains produced ura3 cells while the remaining six strains produced ura5 cells. None of the 12 strains produced both ura3 cells and ura5 cells. All 12 isolates of var. neoformans, however, produced ura5 cells and one of them produced ura3 as well as ura5 cells. A genetic lesion in the URA5 gene of an isolate of C. neoformans var. gattii was confirmed by complement with the cognate URA5 gene of C. neoformans var. neoformans. The ura3 isolates were tentatively identified by their ability to grow on a medium containing uridine but not on a medium with orotic acid or orotidine. Enzymatic assays for orotidine-5'-phosphate decarboxylase activity confirmed the isolates to be ura3 mutants. Hybridization analysis of total DNA, digested with EcoRI or StuI and probed with pURA5g2, revealed the presence of only one copy of URA5 in the strains of either variety, regardless of the prevalence of ura5 mutants. Extensive polymorphism was observed in the restriction patterns of the fragments containing the URA5 locus. The prevalence of spontaneously arising ura3 mutants among the isolates of C. neoformans var. gattii, but not among the isolates of C. neoformans var. neoformans, is one more biological difference that distinguishes the two varieties.

Animals↗
PubMed1992

Can Dexter cultures support stem cell proliferation?

The in vitro culture of mouse bone marrow (Dexter cultures) has allowed a detailed analysis of the biology of murine hematopoiesis. However, attempts to develop stable long-term human bone marrow cultures have been unsuccessful. Available culture systems all have finite and relatively short lifetimes. The reasons for the limited longevity are unknown. Utilizing computer-assisted integration techniques, we have theoretically simulated culture cell production kinetics to help identify factors that may be responsible for culture decay, as well as to suggest possible means of improving culture longevity. The simulation demonstrates that removal of stem cells is a possible mechanism leading to culture decline. Under the standard bone marrow culture conditions, even with a high stem cell renewal rate, the cultures appear to be destined to fail. Thus, the development of proper sampling techniques or improved stem cell retention may be critical to obtain successful long-term cultures.

Animals↗
PubMed1991

Rapid method to extract DNA from Cryptococcus neoformans.

A rapid and easy method for the extraction of total cellular DNA from Cryptococcus neoformans is described. This procedure modifies and considerably simplifies previously reported methods. Numerous steps were either eliminated or replaced, including preincubations with cell wall permeability agents such as beta-mercaptoethanol and dithiothreitol. The commercially available enzyme preparation Novozyme 234 was found to contain a potent concentration of DNases which actively degrade DNA. Degradation and loss of DNA was prevented by maintaining a high concentration of EDTA in the lysing solution. This procedure resulted in high yields (150 to 200 micrograms of DNA from 100 ml of culture) of good-quality (undegraded), high-molecular-weight DNA which was readily digested by restriction endonucleases, making it suitable for use in various molecular applications.

Cryptococcus neoformans↗
PubMed1990

Chlorpromazine-induced immunopathy: progressive increase in serum IgM.

Long-term chlorpromazine therapy has been associated with the asymptomatic development of a high incidence of antinuclear antibodies, coagulation inhibitors, and increased serum levels of IgM. The purpose of this study has been to characterize the natural history of this chlorpromazine-induced (CPZ) immunopathy. To this end we carried out a prospective study of schizophrenic patients with the immunopathy to compare the effect of continuing CPZ versus switching to haloperidol therapy. Although no marked differences were noted between the 2 groups at the end of 5 years, 6 of 29 patients who continued to receive CPZ, as compared to none of 14 patients on haloperidol, had progressive elevations of serum IgM. In spite of a high incidence of antinuclear antibodies, none of the patients developed a lupus-like syndrome. One patient, however, who had been maintained on CPZ for more than 15 years, developed Waldenström macroglobulinemia, as characterized by an IgM monoclonal gammopathy and a lymphocyte immunoglobulin heavy and kappa light chain gene rearrangement. Another CPZ-treated patient developed immune thrombocytopenia. Based on the potential serious sequelae of prolonged stimulation of the immune system by CPZ, we recommend that patients who develop an increase in serum IgM while on CPZ be switched to other types of anti-psychotic medications.

Antibodies, Antinuclear↗
PubMed1989

Upper and lower bounds from the maximum principle. Intracellular diffusion with Michaelis-Menten kinetics.

Analytical bounding functions for diffusion problems with Michaelis-Menten kinetics were recently presented by Anderson an Arthurs, 1985 (Bull. math. Biol. 47, 145-153). Their method, successful to some extent for a small range of parameters, has the disadvantage of providing a weak upper bound. The optimal approach for the use of one-line bounding kinetics is presented. The use of two-line bounding kinetics is also shown, in order to give sufficient accuracy in those cases where the one-line approach does not provide satisfactory results. The bounding functions provide excellent upper and lower bounds on the true solution for the entire range of kinetic and transport parameters.

Biological Transport↗
PubMed1989

Restriction fragment polymorphism in mitochondrial DNA of Cryptococcus neoformans.

The restriction patterns of mitochondrial DNA from 20 isolates of the two varieties of Cryptococcus neoformans were compared. The patterns exhibited extensive heterogeneity among the isolates regardless of their serotype or varietal status. Hybridizations with cloned fragments of the conserved cytochrome oxidase gene from Saccharomyces cerevisiae exhibited at least seven patterns among the 20 isolates. There were, however, similarities in the restriction patterns among isolates within the same serotype that were not shared by isolates of other serotypes. Intra-varietal similarities were observed in the restriction patterns among the isolates of C. neoformans var. neoformans which were not present in the restriction patterns among the isolates of C. neoformans var. gattii. Hybridization of some cloned mitochondrial DNA fragments to total DNA digests of various isolates revealed polymorphic as well as variety-specific patterns of homology. These findings agree with the antigenic heterogeneity among the isolates and support the current taxonomic classification of C. neoformans into two varieties.

Blotting, Southern↗
PubMed1988

Caries inhibition of mixed NaF-Na2PO3F dentifrices containing 1,000 and 2,500 ppm F: 3-year results.

The 3-year DMFS increments of 2,509 children were compared. Group 1 used a conventional Na2PO3F dentifrice (1,000 ppm F) and served as the active control. Groups 2 and 3 used mixed-fluoride dentifrices containing equimolar amounts of NaF and Na2PO3F, providing total fluoride concentrations of 1,000 and 2,500 ppm F, respectively. Dentifrice use was unsupervised in the subjects' homes. There were no statistically significant differences (F-test) between the 3-year DMFS increments of the dentifrice groups, nor were there any significant differences between the dentifrice groups when the analysis included subject compliance and caries risk.

Child↗
PubMed1977

The relationship between rumen bacterial growth, intake of dry matter, digestible organic matter and volatile fatty acid production in buffalo (Bos bubalis) calves.

1. The production rates of bacteria in the rumen of buffalo (Bos bubalis) calves were estimated using an isotope-dilution technique. A series of fifteen experiments was done with animals given green maize and nine experiments with animals given cowpea (Vigna unguiculata). 2. The turnover time ranged from 205 to 567 min in the group given green maize and from 330 to 648 min in animals offered cowpea. The production rates of bacteria were (mean +/- SE; g/d) 145.77 +/- 7.240 and 237.09 +/- 11.847 in animals given green maize and cowpea respectively. 3. There was a significant correlation between bacterial production rates and dry matter intake, digestible organic matter and total volatile fatty acids formed in the rumen. 4. Regression equations obtained for the two foodstuffs were different suggesting that the bacterial growth rate may vary depending upon the quantity and quality of foodstuff digested and possibly the ratio nitrogen:energy of the foodstuff.

Animal Feed↗
PubMedDate not supplied

Application of population balance model to the loss of hybridoma antibody productivity.

A simple dynamic model has been applied to explain the population dynamics of monoclonal antibody (MAb) producing (producer) and nonproducing hybridoma cells (nonproducer) coexisting in culture. The events of mutation or loss of genes associated with antibody synthesis have been incorporated into the model to account for the conversion of a producer to a nonproducer. The model shows that the cell population is not necessarily dominated by the nonproducer, and a steady balance of producer and nonproducer populations can be achieved. A nonproducer population is undesirable, and cultivation strategies to maximize MAb production are suggested, taking into account the dynamics of a nonproducer population.

Antibodies, Monoclonal↗
PubMedDate not supplied

Transmission of enteric non-A, non-B hepatitis virus in Macaca mulatta monkeys by intraportal route: subsequent passages of HEV virus.

Macaca mulatta monkeys have been used for the transmission of enteric non-A, non-B hepatitis (HEV) virus by intraportal route. Subsequent passages of HEV virus have been completed in these monkeys. In the first passage, 2 monkeys were inoculated by intra-portal route with 27-34 nm virus-like particles (VLP) obtained from known epidemics of HEV hepatitis in India, and biochemical and serological changes in the blood, histological changes in the liver and excretion of 27-34 nm VLP in the stool were studied. Results were compared with those of 4 negative control monkeys inoculated with stool extracts from healthy individuals. The second passage of 27-34 nm VLP was carried out on 2 monkeys using pools of stool suspension positive for 27-34 nm VLP from first passaged animals. Similarly, the third passage of 27-34 nm VLP was completed intraportally in another monkey. All monkeys developed acute hepatitis, as evidenced by transient elevation of aminotransferase, histopathological changes in the liver, development of antibodies aggregating 27-34 nm VLP and excretion of 27-34 nm VLP in stools. No control monkeys developed these features.

Animals↗