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Biomedical subjects

N Ramakrishna

Publications and source records attributed to N Ramakrishna.

36 records · Page 2Linked to original sources
PubMed1987

beta-Amyloid gene is not present in three copies in autopsy-validated Alzheimer's disease.

Recently, it has been suggested that Alzheimer's disease is associated with a duplication of the amyloid precursor protein gene localized to chromosome 21q21. In this study, a cloned DNA probe (B2.3), complementary to the sequence coding the beta-amyloid peptide, and DNA polymorphisms adjacent to this sequence were used to determine the number of copies of the beta-amyloid gene in DNA isolated from human blood and brain. Individuals with trisomy 21 (Down syndrome) who were heterozygous for the polymorphisms showed a gene-dosage effect, with one allele exhibiting twice the autoradiographic intensity as the other. Heterozygous individuals with Alzheimer's disease and controls showed equal intensities of the two allelic bands, suggesting that there are only two copies of the beta-amyloid gene in these individuals. In individuals with Alzheimer's disease and in controls who were homozygous for these polymorphisms, the number of copies of the beta-amyloid gene was determined by comparing the autoradiographic intensity of beta-amyloid alleles to that of DNA fragments detected by a reference probe. No difference was detected between these two groups.

Alzheimer Disease↗
PubMed1987

Molecular cloning and characterization of a cDNA encoding the cerebrovascular and the neuritic plaque amyloid peptides.

Deposits of amyloid fibers are found in large numbers in the walls of blood vessels and in neuritic plaques in the brains of patients with Alzheimer disease and adults with Down syndrome. We used the amino acid sequence of the amyloid peptide to synthesize oligonucleotide probes specific for the gene encoding this peptide. When a human brain cDNA library was screened with this probe, a clone was found with a 1.7-kilobase insert that contains a long open reading frame coding for 412 amino acid residues including the 28 amino acids of the amyloid peptide. RNA gel blots revealed that a 3.3-kilobase mRNA species was present in the brains of individuals with Alzheimer disease, with Down syndrome, or with no apparent neurological disorders. Southern blots showed that homologous genes are present in the genomic DNA of humans, rabbits, sheep, hamsters, and mice, suggesting that this gene has been conserved through mammalian evolution. Localization of the corresponding genomic sequences on human chromosome 21 suggests a genetic relationship between Alzheimer disease and Down syndrome, and it may explain the early appearance of large numbers of neuritic plaques in adult Down syndrome patients.

Alzheimer Disease↗
PubMed1984

The complete DNA sequence and regulatory regions of the Bacillus licheniformis spoOH gene.

We have determined the sequence of a 1228 base-pair cloned DNA fragment from Bacillus licheniformis capable of specifically complementing mutations in the spoOH gene, which is required for the early stage of sporulation in B. subtilis. The sequence has only one long open reading frame consisting of 168 codons. In vivo and in vitro transcription mapping studies indicate the size of complementary RNA to be around 1 kb with the 5' initiation site at base 79 and the 3' termination site in the area of base 1138. This indicates the presence of a 5' untranslated RNA and a fairly long 3' extension. The promoter sequence of this gene is 5'TATAAT3' at -10, and 5'TTGACG3' at -35, a typical E. coli-like promoter sequence, and is transcribed in vitro specifically only by RNA polymerase containing delta 55 and not delta 37-containing holoenzyme.

Amino Acid Sequence↗
PubMed1984

Bacillus subtilis spo0H gene.

A 2.8-kilobase fragment of the Bacillus subtilis chromosome containing a functional spo0H gene was cloned by using a modification of the helper system described by T. Gryczan and co-workers (T. Gryczan, S. Contente, and D. Dubnau, Mol. Gen. Genet. 177:459-467, 1980). The chromosomal segment specifically complements spo0H mutations in recE4 strains and when integrated into the chromosome of Rec+ strains maps in the spo0H region of the B. subtilis genome. A deletion within the transcribed region of the cloned spo0H gene was constructed which abolishes its spo0H+-complementing activity. DNA sequences containing this deletion were introduced into a B. subtilis Rec+ strain containing the spo0H75 mutation. The absence of recombination between the deletion and the spo0H mutation indicates that both reside in the same gene. There is homology between the B. subtilis spo0H gene and a 1.2-kilobase chromosomal fragment from Bacillus licheniformis which also complements B. subtilis spo0H mutations. In vivo transcription mapping experiments have shown that the B. subtilis spo0H gene is transcribed during vegetative growth as well as during sporulation.

Bacillus subtilis↗
PubMed1981

Cloning of an early sporulation gene in Bacillus subtilis.

A 0.8-megadalton BglII restriction fragment of Bacillus licheniformis cloned into the BglII site of plasmid pBD64 can complement spo0H mutations of Bacillus subtilis. The clone was isolated by selecting for the Spo+ phenotype and antibiotic resistance, using the helper system described by Gryczan et al. (Mol. Gen. Genet. 177:459-467, 1980). The insert is functional in both orientations and thus presumably has its own promoter. A deletion generated within the 0.8-megadalton insert by HindIII restriction and subsequent religation eliminates the ability of the cloned fragment to complement spo0H mutations. The cloned B. licheniformis deoxyribonucleic acid segment specifies the synthesis, in minicells, of a polypeptide of approximately 27,000 daltons. This protein is observed with both orientations, but not when the HindIII deletion is present in the cloned B. licheniformis chromosomal fragment. We have also demonstrated that ribonucleic acid complementary to the cloned B. licheniformis sporulation gene is transcribed in B. licheniformis both during vegetative growth and sporulation.

Bacillus↗
PubMed1979

Surgery for variceal bleeding in cirrhosis: a review of our experience and present concepts.

The major cause of portal hypertension in Western countries is nutritional cirrhosis (parenchymal block) related to alcoholism. A third of those patients die of variceal bleeding when increased pressure within the varices precipitates bleeding. Construction of portal systemic shunts is aimed at reducing the pressure within the varices and thereby decreasing the risk of bleeding. However, it increases the incidence of hepatic encephalopathy and hence should be used only in patients who have bled. The remaining function appears to be the main factor that determines survival and the incidence of encephalopathy in obese individuals. Portacaval shunts almost completely eliminate the risk of bleeding. There is a greater incidence of hepatic encephalopathy with this procedure than with other shunts. The splenorenal shunt and the distal splenorenal shunt appear to work well in selected patients. Technically, it is a more difficult procedure. The interposition mesocaval shunt is technically easier and is also helpful in patients with ascites. Its post-shunt encephalopathy rate, however, is higher than the splenorenal shunt or the distal splenorenal shunt, though less than the portacaval shunts. Experience with the newer arterialized portacaval and coronary caval shunts is limited. A non-shunt procedure, such as the one described by Sugiura, with impressive results and follow-up may become more acceptable as experience grows.

Adult↗
PubMedDate not supplied

The effects of fungal competition on colonization of barley grain by Fusarium sporotrichioides on T-2 toxin formation.

Colonization of barley grain by Fusarium sporotrichioides and T-2 toxin formation in the presence of Aspergillus flavus, Penicillium verrucosum, and Hyphopichia burtonii were studied at 20 and 30 degrees C and at 0.97, 0.95 or 0.90 aw during 3 weeks' incubation. Colonization of grain was assessed from frequency of seed infection and numbers of colony forming units (cfu) produced and by observation of hyphal extension on the grain surface from germinating spores while concentrations of T-2 toxin were determined by enzyme-linked immunosorbent assay using monoclonal antibodies. Germination of F. sporotrichioides spores was unaffected by the presence of other species under all conditions. However, subsequent colonization of barley grain by F. sporotrichioides was either completely inhibited or markedly decreased by the the presence of other fungi irrespective of the aw, temperature or competing species involved. T-2 toxin production occurred only at 20 degrees C and 0.97 or 0.95 aw, and mostly within the first 7 days: production of T-2 toxin by F. sporotrichioides was significantly greater in the presence of A. flavus and P. verrucosum throughout the 3-week incubation period under most conditions. T-2 toxin production was only slightly decreased by the presence of H. burtonii, despite the apparent lack of growth of F. sporotrichioides.

Aspergillus flavus↗
PubMedDate not supplied

Monoclonal antibody-based enzyme linked immunosorbent assay of aflatoxin B1, T-2 toxin, and ochratoxin A in barley.

Aflatoxin B1 (B1), T-2 toxin (T2), and ochratoxin A (OA) were assayed in a single extract from barley grain by using competitive enzyme linked immunosorbent assays (ELISAs) with monoclonal antibodies. B1 and T2 monoclonal antibodies were conjugated to horseradish peroxidase for direct competitive ELISA while an indirect competitive ELISA was used for OA determination. The competitive ELISA detected 0.1 ng/mL of B1, 10 ng/mL of T2, or 1 ng/mL of OA. Acetonitrile-0.5% KCl-6% H2SO4 (89 + 10 + 1) extracts of barley grain either were diluted 1:10 for direct assay or were subjected to a simple liquid-liquid cleanup procedure to concentrate the extract 10:1 before assay. For cleanup, water was added to the acetonitrile extract to partition water-soluble interfering substances, and then the mycotoxins were re-extracted with chloroform. The chloroform extract was evaporated to dryness and redissolved in Tris HCl buffer for ELISA. The mean recoveries from barley spiked with 4-60 ng/g of B1, 50-5000 ng/g of T2, and 5-500 ng/g of OA were, respectively, 93.8, 80.6, and 95.8%. The mean within-assay, inter-assay, and subsample coefficients of variation by ELISA of barley grain colonized with toxigenic fungi were less than 12% for B1 and OA but as high as 17% for T2.

Aflatoxin B1↗