Search PubMed⌕ Search

Biomedical subjects

A Das

Publications and source records attributed to A Das.

At least 325 records · Page 18Linked to original sources
PubMed1990

Chromosome inversions in Indian Drosophila melanogaster.

Ten laboratory stocks of Drosophila melanogaster initiated from females collected in different localities in India were analysed for chromosome inversions. Six inversions were found to be present, three in 2L, one in 2R, one in 3L and one in 3R. Out of these six inversions, three are new and are being reported for the first time. Furthermore, this is the first report of inversion polymorphism in Indian D. melanogaster. The persistence of inversion polymorphism in our laboratory stocks of D. melanogaster which were maintained for more than one year under laboratory conditions, suggests some heterotic advantage of inversion heterozygotes.

Animals↗
PubMed1990

An analysis of the role of host factors in transcription antitermination in vitro by the Q protein of coliphage lambda.

We used two different approaches to study the requirement for Escherichia coli Nus factors for the activity of bacteriophage lambda late antiterminator Q. Using an in vitro coupled transcription-translation assay, based on Q-dependent synthesis of galactokinase from a pR'-tR'-galK template, we showed that mutations in the host nusB and nusE genes do not affect Q activity. A mutation in nusA (nusA1) only partially affects Q action at all temperatures tested. Defective Q function in the nusA1 mutant extract could be restored by the addition of pure NusA but not by excess Q. In a pure transcription system, measurement of the run-off transcript produced by Q-mediated suppression of tR' revealed that NusA is greatly stimulatory to Q activity, whereas NusB and S10, in the presence or absence of NusA, have no effect. Unidentified E. coli factor(s) present in an S30 extract efficiently suppress the natural pausing by RNA polymerase at +15, +16 of pR' without affecting Q activity. These results show that NusA is the only host protein that directly participates in Q function.

Bacterial Proteins↗
PubMed1990

Sorbinil does not prevent galactose-induced glomerular capillary basement membrane thickening in the rat.

We investigated the role of the polyol pathway in the pathogenesis of glomerular basement membrane thickening in galactosaemic rats, an animal model that develops basement membrane lesions comparable to those of human diabetic subjects. Normotensive Wistar-Kyoto rats fed a 30% galactose diet for nine months developed significant glomerular basement membrane thickening by comparison with rats on a control test diet (p = 0.008). However, addition of an aldose reductase inhibitor, sorbinil (250 mg/kg diet), to the galactose diet did not prevent the increase in glomerular basement membrane thickness. Furthermore, by using a quantitative electron microscopic immunogold technique, we examined biochemical alterations in the composition of glomerular basement membranes in this animal model. The labelling density (comparable to relative concentration) of collagen type IV in thickened glomerular basement membranes of galactosaemic animals was significantly increased by comparison to those of control rats (p = 0.015). However, there was no significant difference in labelling densities of laminin and heparan sulfate proteoglycan core protein of these animals. Thus, our results indicate that an increase in glomerular basement membrane thickness accompanied by an increase in the labelling density of collagen type IV occurs in the galactosaemic rats, but this thickening is not prevented by sorbinil at the dose used in this experiment. Our study raises the strong possibility that glomerular basement membrane thickening in galactosaemic rats may not be due to excessive polyol pathway activity.

Aldehyde Reductase↗
PubMed1990

Floral determination in the terminal bud of the short-day plant Pharbitis nil.

Temporal and spatial aspects of floral determination in seedling terminal buds of the qualitative short-day plant Pharbitis nil were examined using a grafting assay. Floral determination in the terminal buds of 6-day-old P. nil seedlings is rapid; by 9 hr after the end of a 14-hr inductive dark period more than 50% of the induced terminal buds grafted onto uninduced stock plants produced a full complement of flower buds. When grafted at early times after the end of the dark period the terminal buds of induced plants produced three discrete populations of plants: plants with no flowers, plants with two axillary flowers at nodes 3 and 4 and a vegetative terminal shoot apex, and plants with five to seven flowers including a terminal flower. The temporal relationship among these populations of plants produced by apices grafted at different times indicates that under our conditions, the region of the terminal bud that will form the axillary buds at nodes 3 and 4 becomes florally determined prior to floral determination of the region of the terminal bud giving rise to the nodes above node 4.

Darkness↗
PubMed1990

Increases in collagen type IV and laminin in galactose-induced retinal capillary basement membrane thickening--prevention by an aldose reductase inhibitor.

Biochemical alterations in the composition of retinal capillary basement membrane components were investigated in galactosemic rats, an animal model that develops basement membrane lesions comparable to those of diabetic retinopathy. Normotensive Wistar-Kyoto rats fed a 30% galactose diet for 9 months developed significant thickening of retinal capillary basement membranes by comparison with animals fed a control test diet (P less than 0.001), or animals on a diet containing 30% galactose and 250 mg kg-1 of the aldose reductase inhibitor sorbinil (P less than 0.001). A quantitative electron microscopic immunogold technique applied on ultrathin sections of the retinas of these animals showed that the labeling densities of collagen type IV and laminin per unit cross-sectional area (which is presumably proportional to the concentrations of these molecules) were significantly increased in the retinal capillary basement membranes of galactose-fed rats, compared with animals on the control test diet. Increases in these two components of basement membranes were prevented by addition of sorbinil to the diet. However, there was no significant change in the labeling density of heparan sulfate proteoglycan (HSPG) core protein in the basement membranes of galactose-fed rats in comparison to animals on either the control diet or galactose-sorbinil diet. Two types of striated fibrillar materials were frequently found in areas of focal thickening of basement membranes of galactose fed rats only. Thinner fibrils reacted strongly with collagen type III antibody, whereas thicker fibrils reacted weakly with collagen type I antibody. Our results indicate that there is an increase in labeling densities of collagen type IV and laminin in thickened basement membranes of retinal capillaries of galactosemic rats along with the expression of interstitial collagens like collagen type III and an abnormal collagen that weakly cross-reacts with antibody to collagen type I, and these effects of galactosemia on the basement membranes are preventable by an aldose reductase inhibitor.

Aldehyde Reductase↗
PubMed1990

Production of L-dopa by Aspergillus terreus.

Production of L-DOPA by the activity of tyrosinase from a strain of Aspergillus terreus 104 was investigated. Effects of substrate (L-tyrosine) concentrations, its mode of feeding to the assay mixture and also the effects of L-ascorbic acid and other antioxidants on the production rate of L-DOPA were studied. The parameters for optimal production of L-DOPA with a maximum conversion of 85% of 0.1% L-tyrosine were determined.

Antioxidants↗
PubMed1990

virG, an Agrobacterium tumefaciens transcriptional activator, initiates translation at a UUG codon and is a sequence-specific DNA-binding protein.

The Agrobacterium tumefaciens Ti plasmid virG locus, in conjunction with virA and acetosyringone, activates transcription of the virulence (vir) genes. Insertional and deoxyoligonucleotide-directed mutagenesis studies showed that both octopine and nopaline Ti plasmid virG genes initiate translation at a UUG codon. VirG protein initiated at this UUG codon was found to be 241 amino acid residues in length and had an apparent molecular mass of 27.1 kilodaltons. A Salmonella typhimurium trp-virG transcriptional fusion was constructed to overproduce VirG. Agrobacterium cells containing this gene fusion showed a large increase in virG activity in the presence of virA and acetosyringone. Since the trp promoter is not under virA-virG control, this result indicates that modification of VirG is necessary for its full activity. VirG overproduced in Escherichia coli was purified from inclusion bodies. It was found to be a DNA-binding protein that preferentially bound DNA fragments containing the 5' nontranscribed regions of the virA, -B, -C, -D, and -G operons. Significant specific binding to the 5' nontranscribed region sequences of virE was not detected. DNase I footprinting of the upstream regions of virC-virD and virG showed that VirG binds to sequences around the vir box region.

Bacterial Proteins↗
PubMed1990

Inversion polymorphism in Indian natural populations of Drosophila melanogaster.

Six natural populations (three urban and three rural) of Drosophila melanogaster from India were analysed for chromosome inversions, revealing the presence of 19 different paracentric autosomal inversions. One new inversion has also been detected in a laboratory stock established from flies collected from Kerala. In total 20 different paracentric inversions in Indian D. melanogaster have been detected during the present study, and of these, 4 are common cosmopolitans; 2 are rare cosmopolitans; 7 are recurrent endemics; and 7 are unique endemics. The quantitative data clearly show that the urban populations are different from the rural ones with respect to inversion polymorphism.

Animals↗
PubMed1990

Proliferative response and macromolecular synthesis by ocular cells cultured on extracellular matrix materials.

To investigate the effects of extracellular matrix components on cellular function, we cultured several types of ocular cells on substrates composed of extracellular matrix materials that were layered on culture dishes either as dried films or as gels. We measured cellular proliferation on these substrates and on a series of gels composed of varying proportions of rat tail tendon type I collagen and Matrigel, a commercially available extract of a basement membrane-producing murine tumor. In addition, we studied the biosynthesis of collagens and of proteoglycans by these cultured cells using [3H]-L-proline and [35S]-sulfate. The proliferative abilities of the various types of ocular cells on the dried film substrates, on uncoated plastic culture vessels, and on pure type I collagen gel, were similar. However, proliferation of ocular cells cultured on gels composed of greater than or equal to 90% Matrigel was markedly reduced. There was little or no inhibition of growth of two types of non-ocular cells: rat C6 astrocytoma cells, and human dermal fibroblasts. Histologic studies showed that the ocular cells tested often formed long strands and capillary-like tubes, and tended to "burrow" beneath the surface of substrates containing high percentages of Matrigel. Fibroblasts infrequently formed tubes, and exhibited the burrowing property also on gels containing primarily type I collagen, while C6 cells showed neither of these behaviors on any of the matrices tested. The elution pattern of newly synthesized [3H]-labeled and [35S]-labeled macromolecules produced by all of the cultured cell types, and detected by Sepharose CL-4B chromatography in the medium and in the cell layer plus matrix fractions did not vary following culture on the different substrates. Approximately twofold more of the newly synthesized collagens and proteoglycans were deposited in the cell layer plus matrix, and proportionately less appeared in the medium, when cells were cultured on type I collagen gels and on Matrigel than on the dried film substrates. These experiments demonstrate the influence of the extracellular matrix on several aspects of cell behavior, and provide further evidence that modification of the composition of the extracellular matrix may be an important determinant of normal or pathological cell function.

Animals↗
PubMed1990

Action of an RNA site at a distance: role of the nut genetic signal in transcription antitermination by phage-lambda N gene product.

The N gene product of Escherichia coli phage lambda is a transcriptional activator that captures the host RNA polymerase and modifies it to a termination-resistant form, permitting gene expression in two large polycistronic operons of the phage genome. Antitermination in vitro requires at least one host factor called NusA, which directly binds the N protein as well as RNA polymerase, and also a transcribed cis-acting site known as nut, within which lies the hypothesized N-recognition signal, boxB. BoxB is an interrupted palindrome capable of forming a hairpin in the mRNA. Inhibition studies with complementary DNA oligonucleotides provide evidence for a direct role of the boxB hairpin in antitermination. Kinetic studies of transcript elongation reveal that the boxB hairpin does not induce an appreciable pause to hold polymerase captive for engagement by N and NusA. Moreover, the efficiency of antitermination remains virtually the same whether N and NusA are added early, prior to nut site transcription, or added later, after the polymerase has already transcribed past the nut site. After transcription of the nut site, RNA polymerase remains susceptible to modification by N and NusA for an appreciable amount of time and distance, and the nut site DNA becomes dispensable for this modification. These results lead to the hypothesis that the boxB RNA hairpin acts in a manner analogous to the DNA enhancers, binding N and mediating a productive polymerase-NusA-N interaction by mRNA looping.

Bacterial Proteins↗
PubMed1990

Pericyte coverage of retinal and cerebral capillaries.

We performed electron microscopic morphometric analyses on capillaries from macular and peripheral retinas of five adult cynomolgous monkeys and three elderly human subjects. Measurements from the monkey retinal capillaries were compared to those made on capillaries from frontal, temporal, parietal, and occipital cerebral cortex of the same animals. We measured the percent coverage of the endothelial lining of the capillaries by pericyte processes, as well as the ratio of the cytoplasmic areas of pericytes and endothelial cells. In addition, we compared the thickness of the capillary basement membranes in three regions: overlying pericytes; overlying endothelial cells; and interposed between pericytes and endothelial cells. In both monkey and human retinas, pericyte processes covered greater than 85% of the circumference of the capillary endothelial tube, whereas pericyte coverage of monkey cerebral capillaries was highly significantly (P less than 0.001) less than that of capillaries in either the macular or peripheral retina. The ratio of pericyte to endothelial cell cytoplasmic areas also was lower in the monkey cerebral cortex than in the retina, though the statistical significance was less than that of the length measurements. In all tissues measured, both from monkeys and humans, the portions of the capillary basement membranes interposed between pericytes and endothelial cells were highly significantly (P less than 0.0001) thinner than the regions of capillary basement membranes covering pericytes and endothelial cells. Considering functions that have been proposed for pericytes, these measurements suggest that regional control of microcirculatory flow and of blood-tissue barrier integrity, as well as control of endothelial cell proliferation, should be much greater in the retina than in the cerebral cortex. Thinner basement membranes between pericytes and endothelial cells may permit more cell membrane contacts between these cells, thus facilitating such control.

Aged↗
PubMed1989

Restoration of a translational stop-start overlap reinstates translational coupling in a mutant trpB'-trpA gene pair of the Escherichia coli tryptophan operon.

The trpB and trpA coding regions of the polycistronic trp mRNA of Escherichia coli are separated by overlapping translation stop and start codons. Efficient translation of the trpA coding region is subject to translational coupling, i.e., maximal trpA expression is dependent on prior translation of the trpB coding region. Previous studies demonstrated that the trpA Shine-Dalgarno sequence (within trpB) and/or the location of the trpB stop codon influenced trpA expression. To examine the effect of stop codon location specifically, we constructed plasmids in which different nucleotide sequences preceding the trpA start codon were retained, and only the reading frame was changed. When trpB translation proceeded in the wild type reading frame and terminated at the normal trpB stop codon, trpA polypeptide levels were elevated over the levels observed when translation stopped before or after the natural trpB stop codon. The proximity of the trpB stop codon to the trpA start codon therefore markedly influences trpA expression.

Base Sequence↗
PubMed1989

Sequence-specific recognition of RNA hairpins by bacteriophage antiterminators requires a conserved arginine-rich motif.

We have dissected the protein and nucleic acid determinants that direct a group of transcriptional antiterminators to their specific target operons. These antiterminators, the N gene products of phages lambda, 21, and P22, function solely with their respective recognition sites, nut, to modify RNA polymerase to a termination-resistant form. We demonstrate that a unique hairpin sequence within each nut site, called boxB, confers genome specificity by interacting with a small amino-terminal domain of the cognate N protein. This interaction is dependent upon an arginine-rich subdomain, which is conserved not only among the N proteins but also in many RNA binding proteins from ribosomes and RNA virus capsids. Notably, this motif constitutes an essential domain of the HIV protein Tat whose function as a trans-activator requires a specific hairpin sequence.

Amino Acid Sequence↗
PubMed1989

Delineation of the regulatory region sequences of Agrobacterium tumefaciens virB operon.

A virB-lacZ translational fusion was constructed to monitor expression of the Agrobacterium tumefaciens virB operon. Expression of the fusion gene was dependent on the presence of pTiA6 virA, virG, and a plant factor acetosyringone. Analysis of deletion mutants, constructed by exonuclease Bal31 digestion, showed that 68 residues upstream of the virB transcription initiation site was necessary for its expression. A TT----CC substitution at positions -62 and -61 led to a 7 fold reduction in virB expression. The virB upstream region contains a tetradecameric sequence, dPuT/ATDCAATGHAAPy (D = A, G or T; H = A, C or T), that is conserved in the non-transcribed regions of all vir genes. Alteration of the position of this sequence relative to the promoter region sequences had a drastic negative effect on virB expression.

Base Sequence↗
PubMed1989

Fine-needle aspiration cytology of sacrococcygeal chordoma.

The fine-needle aspiration cytology (FNAC) of four cases of chordoma that were diagnosed preoperatively is presented. One of the cases showed anaplastic components along with the classical features of chordoma; this is probably the second case diagnosed with these features on FNAC. The cytologic features of classical chordoma include conspicuous extracellular matrix in the background. Polygonal cells, dissociated and in small groups, were identified in all cases. Physaliphorous cells were also prominently found in these cases. In addition, the case with anaplastic features showed very bizarre cells with profound multinucleation and the presence of intranuclear cytoplasmic inclusions. The diagnosis of chordoma was possible because of a high index of suspicion on clinical grounds and the use of special staining for confirmation.

Aged↗