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Biomedical subjects

S Guha

Publications and source records attributed to S Guha.

At least 73 records · Page 4Linked to original sources
PubMed1992

Improved plasmids containing the Escherichia coli dam gene under the control of the tac promoter.

We report the construction of a series of plasmids containing the dam gene under the control of the tac promoter. Cells containing these plasmids produce about 8 to 10-fold more Dam methyltransferase (Mtase) than the previously used plasmid pTP166 and avoid the use of a high temperature step necessary for the expression of Dam Mtase in the plasmid pDOX1 and thus allow its use for the study of thermosensitive mutants.

Cloning, Molecular↗
PubMed1992

Expression of Escherichia coli dam gene in Bacillus subtilis provokes DNA damage response: N6-methyladenine is removed by two repair pathways.

The dam gene of Escherichia coli encodes a DNA methyltransferase that methylates the N6 position of adenine in the sequence GATC. It was stably expressed from a shuttle vector in a repair- and recombination-proficient strain of Bacillus subtilis. In this strain the majority of plasmid DNA molecules was modified at dam sites whereas most chromosomal DNA remained unmethylated during exponential growth. During stationary phase the amount of unmethylated DNA increased, suggesting that methylated bases were being removed. An ultraviolet damage repair-deficient mutant (uvrB) contained highly methylated chromosomal and plasmid DNA. High levels of Dam methylation were detrimental to growth and viability of this mutant strain and some features of the SOS response were also induced. A mutant defective in the synthesis of adaptive DNA alkyltransferases and induction of the adaptive response (ada) also showed high methylation and properties similar to that of the dam gene expressing uvrB strain. When protein extracts from B. subtilis expressing the Dam methyltransferase or treated with N-methyl-N'-nitro-N-nitroso-guanidine were incubated with [3H]-labelled Dam methylated DNA, the methyl label was bound to two proteins of 14 and 9 kD. Some free N6-methyladenine was also detected in the supernatant of the incubation mixture. We propose that N6-methyladenine residues are excised by proteins involved in both excision (uvrB) and the adaptive response (ada) DNA repair pathways in B. subtilis.

Adenine↗
PubMed1991

The role of glutathione in evaluating the efficacy of antimetabolites in transplanted tumors.

Levels of glutathione (GSH) in tumor cells play an important role in determining the clinical responses to certain anticancer agents. In the present work 5-fluorouracil and 5-fluorodeoxyuridine have been used as antineoplastic agents against transplanted Ehrlich ascites carcinoma. The glutathione levels in the tumor cells and liver tissues of the host animals have been studied by a specific histofluorescence method. Significant changes have been observed in the glutathione level of the host, tumor bearing and treated group of animals, the implications of which have been discussed.

Animals↗
PubMed1990

The role of polyamines as a marker of tumor progression and regression in experimental tumors.

The pattern of changes in the polyamine spectrum has been studied under the stress of Sarcoma 180, a transplanted tumor growing in the peritoneal cavity of mice. Retinol, a known inhibitor of ornithine decarboxylase, was used to modulate tumor growth pattern and subsequent changes in the level of polyamines. The polyamine levels showed an increase during tumor proliferation. In the treated group, however, the enhanced levels exhibited a tendency to decrease, along with tumor inhibition, indicating that a positive correlation exists between the polyamine content in the red blood cells of mice and the tumor growth pattern.

Animals↗
PubMed1989

Preliminary studies on excretory components of a virulent strain (F-2) of Pseudomonas solanacearum.

The excretory material (EM) was isolated from the culture medium of a virulent strain (F-2) of Pseudomonas solanacearum. Electrophoretic studies depicted the heterogeneous nature of EM and the presence of released lipopolysaccharide in it. Both the exopolysaccharide and the released LPS contained D-galactose as the major sugar constituent together with D-glucose, N-acetyl-D-galactosamine and N-acetyl-D-glucosamine. In addition, L-rhamnose was present as a constituent sugar of the released LPS.

Bacterial Proteins↗
PubMed1988

DNA methyltransferase of Bacillus subtilis Marburg: purification, properties and further evidence of specificity.

Bacillus subtilis Marburg strain displays DNA methyltransferase activity. This enzyme, M.BsuM, methylates cytosine in the sequence 5'-YTCGAR-3' (Y = pyrimidine; R = purine). M.BsuM was purified from the exponentially growing cells of B. subtilis 168M. This enzyme (45 +/- 1 kDa) is monomeric and recognizes only double-stranded DNA. It is inhibited partially by Mg2+, Mn2+ ions and spermidine and almost totally by sodium dodecyl sulfate, urea and agarose. This enzyme methylates specifically the three methylatable sites of the plasmid pBM3. Relaxation of specificity ('star' activity) was observed in the presence of organic solvents. A very low amount of M.BsuM was obtained in the standard Marburg strain. To obtain sufficient enzyme attempts are being made to clone the M.BsuM gene in Escherichia coli by using a constructed plasmid (pBM14) vector. Only one transformant containing a 3-kb insert and showing a low level of expression, was obtained.

Bacillus subtilis↗
PubMed1987

Activation of lymphocytes of normal and tumor bearing mice by mangiferin, a naturally occurring glucosylxanthone.

Mangiferin, a naturally occurring glucosylxanthone, was assessed for its immunomodulatory potential. The phytochemical induced extensive in vitro proliferation of murine splenocytes and thymocytes at the doses of 5-40 micrograms ml-1. Suppression of the proliferative response of the cells was observed with higher doses of mangiferin. Mangiferin also activated the splenocytes of tumor hosts at early and late stages of tumor growth. The Phytohemagglutinin (PHA) and Con A unresponsive splenocytes of advanced tumor bearer proliferated extensively in response to mangiferin. Mangiferin when used with Con A produced additive stimulatory effect and induced heightened DNA synthesis of normal and advanced tumor bearers' splenocytes.

Adjuvants, Immunologic↗
PubMed1986

Concanavalin A-induced agglutination of Ehrlich ascites carcinoma cells during growth of the tumor in mice.

ConA-induced agglutination of Ehrlich ascites carcinoma (EAC) cells during development of the tumor in mice has been studied in vitro. EAC cells were incubated with different concentrations of ConA at 37 degrees C for various intervals of time and the cell aggregates of different sizes were scored under microscope. The older EAC cells (20-day-old) showed a decrease in cytoagglutination with respect to large aggregates formation compared to the younger (10-day-old) ones. The small aggregates formed by the 5-day-old EAC cells are dissociated by competition with alpha-methyl-D-mannoside but the large aggregates are not affected by the sugar treatment. The observed differences in the agglutination patterns are discussed in view of the influence of the lipid content of EAC cells and the ascites fluid on ConA-induced cytoagglutination.

Animals↗