PubMed Health⌕ Search

Biomedical subjects

S Char

Publications and source records attributed to S Char.

17 recordsLinked to original sources
PubMed1998

Does CagA contribute to ulcer pathogenesis in a developing country, such as Sudan?

BACKGROUND AND OBJECTIVE: In Western populations, peptic ulcer disease is closely associated with Helicobacter pylori (H. pylori) strains expressing the CagA antigen. In Africa the prevalence of H. pylori infection and peptic ulcer disease is high, although information regarding potential virulence factors is lacking. This study examines the prevalence of antibodies to CagA both in African patients with dyspepsia who are undergoing gastroscopy, and in asymptomatic healthy African volunteers. METHODS: Eighty two consecutive patients (median age 34 years, range 15-73 years), attending for gastroscopy were studied, of whom 78 (95.1%) were subsequently found to be Helicobacter positive. Three antral biopsies were obtained from each patient and 5 ml of blood was taken for determination of CagA seropositivity using western blot analysis. CagA seropositivity was also determined in 65 H. pylori positive healthy volunteers (median age 30 years, range 18-70 years), with no symptoms or previous history of gastroduodenal disease. RESULTS: Of the 78 H. pylori positive patients, CagA seropositivity was present in all 22 patients with active peptic ulcer disease (100%), in eight of nine patients with duodenitis (89%), in 15 of 19 patients with macroscopic gastritis (78.9%), and in 24 of 28 patients with a normal endoscopy (85.7%). On histological assessment, 46 patients had chronic active gastritis, 29 patients had gastritis with atrophy and three patients had intestinal metaplasia. CagA seropositivity rates were 84.7%, 93% and 100%, respectively, for these groups. In the 89 healthy volunteers studied, 57 of the 65 H. pylori positive subjects (87.7%) were seropositive for the CagA protein. CONCLUSIONS: As in Western countries, CagA seropositivity in this African population was closely related to endoscopic gastroduodenal disease, and to the presence of more advanced histological lesions in the antrum. However, there was also a high prevalence of CagA seropositivity in asymptomatic healthy individuals, suggesting that factors other than CagA predominate in ulcer pathogenesis in this population.

Adolescent↗
PubMed1996

Codon usage in Cryptosporidium parvum differs from that in other Eimeriorina.

Codon usage of Crytosporidium parvum was compared with those of other Eimeriorina Toxoplasma gondii and Eimeria tenella and revealed a biased use of synonymous codons with a preference for NNU (40.0%) and NNA (33.4%). There was no close resemblance of the codon usage of C. parvum to T. gondii (correlation coefficient, r = 0.14) or E. tenella (r = 0.14) but it was similar to Entamoeba histolytica (r = 0.75) and Plasmodium falciparum (r = 0.5). Analysis of the codon usage in homologous gene sequences (actin, beta-tubulin) also failed to reveal a close relationship between C. parvum and T. gondii or E. tenella. The low usage codons in C. parvum were most frequently used codons in T. gondii and E. tenella. These observations are consistent with 18S rRNA sequence analysis which shows no close relationship of Cryptosporidium with other Eimeriorina (Sarcocystis, Toxoplasma and Eimeria) and questions the validity of the current classification of C. parvum.

Actins↗
PubMed1993

Impaired IgA response to Giardia heat shock antigen in children with persistent diarrhoea and giardiasis.

The serum antibody response in Gambian children with persistent diarrhoea and giardiasis has been studied. Total serum IgG, IgA, and IgM concentrations were increased in these patients as compared with controls from the same area. Determination of the concentrations of Giardia specific antibodies by enzyme linked immuno adsorbent assay (ELISA), however, revealed that only IgM was raised while those of IgA and IgG were similar to the controls. Analysis of the antigenic determinants of the IgG and IgA responses by immunoblotting showed that patients with chronic infection unlike those who clear the infection have no IgA response to a 57 kDa Giardia heat shock antigen. The association of high concentrations of Giardia specific IgM, low concentrations of Giardia specific IgA and IgG and inability to clear the infection suggests that the switch from an IgM to an IgG or IgA response is inefficient.

Animals↗
PubMed1992

Codon usage in Entamoeba histolytica.

The codon usage of 10 E. histolytica genes comprising 4455 codons was analysed. The codon usage revealed an extremely biased use of synonymous codons with a preference for NNU (44%) and NNA (41.4%) codons. Codons CGG (arg), AGG (arg) and CCG (pro) were absent in the E. histolytica genes examined. The codon usage of E. histolytica resembled that of Plasmodium falciparum.

Animals↗
PubMed1992

An immunodominant antigen of Giardia lamblia is a heat shock protein.

In this study we demonstrate that an immunodominant antigen of Giardia lamblia is a heat shock protein. The expression of the antigen was induced not only by heat shock but also when Giardia trophozoites were placed in media more closely resembling the environment in the host, indicating that this antigen may play an important role in host-parasite interactions.

Animals↗
PubMed1991

Sequence changes in both flanking sequences of a pre-tRNA influence the cleavage specificity of RNase P.

The cleavage specificities of the RNase P holoenzymes from Escherichia coli and the yeast Schizosaccharomyces pombe and of the catalytic M1 RNA from E. coli were analyzed in 5'-processing experiments using a yeast serine pre-tRNA with mutations in both flanking sequences. The template DNAs were obtained by enzymatic reactions in vitro and transcribed with phage SP6 or T7 RNA polymerase. The various mutations did not alter the cleavage specificity of the yeast RNase P holoenzyme; cleavage always occurred predominantly at position G + 1, generating the typical seven base-pair acceptor stem. In contrast, the specificity of the prokaryotic RNase P activities, i.e. the catalytic M1 RNA and the RNase P holoenzyme from E. coli, was influenced by some of the mutated pre-tRNA substrates, which resulted in an unusual cleavage pattern, generating extended acceptor stems. The bases G - 1 and C + 73, forming the eighth base pair in these extended acceptor stems, were an important motif in promoting the unusual cleavage pattern. It was found only in some natural pre-tRNAs, including tRNA(SeCys) from E. coli, and tRNAs(His) from bacteria and chloroplasts. Also, the corresponding mature tRNAs in vivo contain an eight base pair acceptor stem. The presence of the CCA sequence at the 3' end of the tRNA moiety is known to enhance the cleavage efficiency with the catalytic M1 RNA. Surprisingly, the presence or absence of this sequence in two of our substrate mutants drastically altered the cleavage specificity of M1 RNA and of the E. coli holoenzyme, respectively. Possible reasons for the different cleavage specificities of the enzymes, the influence of sequence alterations and the importance of stacking forces in the acceptor stems are discussed.

Base Sequence↗
PubMed1991

Serum antibody response in children with Giardia lamblia infection and identification of an immunodominant 57-kilodalton antigen.

Giardia lamblia antigens which react with sera from children with G. lamblia infection were investigated by sodium-dodecyl polyacrylamide gel electrophoresis and immunoblotting. Serum IgG, IgM and IgA response to the antigens were immunochemically characterized. Serum antibodies from all giardiasis patients, but none of the controls, was found to react with a 57-kilodalton antigen. The 57 kDa antigen elicited IgG and IgA but not IgM antibodies. The protein nature of the 57 kDa antigen was demonstrated by loss of antibody recognition after trypsin treatment of G. lamblia trophozoites. Subcellular fractionation of G. lamblia trophozoites followed by SDS-PAGE and immunoblotting showed that the 57 kDa antigen was probably not a component of the cytoskeleton.

Animals↗
PubMed1990

The methylation of one specific guanosine in a pre-tRNA prevents cleavage by RNase P and by the catalytic M1 RNA.

Several modified nucleosides were introduced during in vitro RNA synthesis into a pre-tRNA(Ser). The pre-tRNAs were used as substrates for RNase P enzymes. No effects were observed with biotin-8-ATP or [alpha-S]-GPT, whereas with m7GTP, the cleavage reaction was completely inhibited. Analysis of pre-tRNAs which contained m7G at various positions has revealed a single base at the 5'-end of the acceptor stem where this modification absolutely prevents cleavage by catalytic M1 RNA, eukaryotic and prokaryotic RNase P holoenzymes. These results suggest that a critical contact must be made between pre-tRNA substrate and enzyme/ribozyme or that the approach of the potential cleaving agent (a positive magnesium ion) is made impossible by the positive charge at N-7 of the guanosine. In addition, we have shown that a pre-tRNA containing only m7G's can still form a complex with M1 RNA in a gel retardation assay.

Base Sequence↗
PubMed1990

Purification of recombinant Mycobacterium leprae 65-kilodalton antigen and murine antibody responses to intravenously administered recombinant protein.

Recombinant Mycobacterium leprae 65-kilodalton antigen has been purified by a combination of differential solubility, ion-exchange and hydrophobic interaction chromatography, and a method for the quantification of the antigen in large scale protein preparations developed. By injecting large amounts of the recombinant antigen intravenously into mice, a limited degree of specific suppression of antibody-response has been induced.

Animals↗
PubMed1987

The RNA components of Schizosaccharomyces pombe RNase P are essential for cell viability.

The fission yeast Schizosaccharomyces pombe contains in the haploid genome one copy of the gene (designated rrkl) for the RNA components of RNase P. Gene disruption in diploid cells of one copy of rrkl resulted in a moderate reduction of the level of cellular RNase P activity. Haploidization by meiosis demonstrated that rrkl is required for cell growth. Thus, the RNA components of S. pombe RNase P are essential in vivo. This is similar to the situation in Escherichia coli.

Cell Division↗
PubMed1986

Arginyl-tRNA synthetase from Mycobacterium smegmatis SN2: purification and kinetic mechanism.

Arginyl-tRNA synthetase [L-Arg: tRNAArg ligase (AMP forming) EC 6.1.1.19] has been purified to homogeneity from Mycobacterium smegmatis SN2. The enzyme is a monomer of molecular weight 56,000. The kinetic patterns obtained by initial velocity and product inhibition studies are consistent with a rapid equilibrium random ter ter mechanism. Polyamines stimulated the formation of arginyl-tRNA, the stimulation being more significant at sub-optimal Mg2+ concentrations. Initial velocity studies performed in the presence of sub-optimal Mg2+ and spermine also indicated that the kinetic mechanism remained sequential random. Various attempts to reveal the formation of enzyme-bound arginyl-adenylate provided no evidence for its existence. The reverse reaction, i.e., the deacylation of arginyl-tRNA, required both AMP and PPi. This observation is consistent with the mechanism proposed.

Acylation↗
PubMed1985

Purification and kinetic mechanism of lysyl-tRNA synthetase from Mycobacterium smegmatis SN2.

Lysyl-tRNA synthetase [L-lys:tRNAlys ligase (AMP forming) EC:6.1.1.6] has been purified to homogeneity from Mycobacterium smegmatis SN2. The enzyme is a dimer of molecular weight 126,000 and is composed of identical subunits. A detailed analysis of the kinetic mechanism of the lysyl-tRNA synthetase has been carried out. A rapid equilibrium random ter ter mechanism is proposed based on initial velocity and product inhibition studies. There is no evidence for the formation of enzyme-bound lysyl-adenylate. The reverse reaction, studied by the deacylation of lysyl-tRNA, requires the presence of both AMP and PPi. This observation is consistent with the mechanism proposed.

Amino Acyl-tRNA Synthetases↗
PubMedDate not supplied

Codon usage in Giardia lamblia.

A codon usage table for the intestinal parasite Giardia lamblia was generated by analysis of the nucleotide sequences of eight genes comprising 3,135 codons. Codon usage revealed a biased use of synonymous codons with a preference for NNC codons (42.1%). The codon usage of G. lamblia more closely resembles that of the prokaryote Halobacterium halobium (correlation coefficient r = 0.73) rather than that of other eukaryotic protozoans, i.e. Trypanosoma brucei (r = 0.434) and Plasmodium falciparum (r = -0.31). These observations are consistent with the view that G. lamblia represents the first line of descent from the ancestral cells that first took on eukaryotic features.

Animals↗