Search PubMed⌕ Search

Biomedical subjects

V Ramesh

Publications and source records attributed to V Ramesh.

At least 127 records · Page 7Linked to original sources
PubMed1997

An artificial regulatory circuit for stable expression of DNA-binding proteins in a T7 expression system.

We had earlier overproduced the transcription activator protein C of bacteriophage Mu in a phage-T7 expression system. Although we achieved a high level of overproduction, the expression was not consistent. This could be due to the leaky expression of T7 RNA polymerase in the uninduced state. Introduction of pLysS, a plasmid encoding T7 lysozyme, a natural inhibitor of T7 RNA polymerase, resulted in consistent, but extremely low production of the C protein. To overcome this problem, we have devised an artificial regulatory circuit to obtain stabilised, consistent overproduction of C protein. The C-binding site was cloned downstream from the transcription start point of T7 lys. Upon induction, the C protein produced binds to its site with a very high affinity, possibly acting as a transcriptional roadblock for lys. This would overcome the inhibitory effect of T7 lysozyme on T7 RNA polymerase.

Bacteriophage T7↗
PubMed1997

Successful recovery of preimplantation embryos by nonsurgical uterine flushing in the bonnet monkey.

A major limitation to progress in primate embryology is the lack of an adequate supply of preimplantation embryos. We describe a method for recovering preimplantation-embryos in bonnet monkeys (Macaca radiata ) using a nonsurgical uterine flushing technique similar to the one previously employed in rhesus monkeys. Forty cyclic females were screened for cervical cannulation, and 10% of these had an impassable cervix. Eleven females suitable for cannulation were selected, and 27 menstrual cycles were monitored over a 5-mo period. Seventy-one percent of the cycles showed estrogen peaks, which were observed between Days 9 and 14 of the cycle. Following natural mating, uterine flushings were performed on Days 5 to 8 of pregnancy (Day 0 = the day following the estrogen peak). Of the 27 recovery attempts, 9 (33.3%) resulted in the recovery of ovulation products, including those of an unfertilized oocyte and empty zona (2 cases), retarded cleavage-stage (4 to 8-cell) embryos (4 cases), morula (1 case) and blastocysts (2 cases). These results show, for the first time, that the nonsurgical uterine flushing technique can be successfully performed to recover uterine-stage preimplantation embryos from bonnet monkeys.

Journal Article↗
PubMed1997

Chromoblastomycosis in India.

BACKGROUND: Chromoblastomycosis is reported for the first time from the states of Jammu-Kashmir and Bihar along with two additional cases from the states of Assam and Uttar Pradesh. The work carried cut on this disease in the Indian subcontinent is reviewed. METHODS: Relevant mycologic investigations, including direct microscopy, histopathology, and culture, were carried out to study the four cases. Treatment was given to two patients. RESULTS: The duration of the lesions varied from 5 to 32 years. In one case the lesion was a large erythematous plaque on the buttocks extending to the backs of the thighs, and in the others they were hypertrophic lesions on the extremities. Histopathologic study of specimens carried out in three patients revealed the causative organisms. On culture, Cladosporium carrionii was isolated in one and Fonsecaea species in the other three. The lesions in one patient were surgically excised and another patient responded well to a combined regimen of amphotericin B and 5-fluorocytosine. CONCLUSIONS: Although chromoblastomycosis is widely distributed in India, many patients remain undiagnosed due to a lack of proper facilities. Treatment is difficult and most patients are not able to afford the drugs prescribed for this condition.

Adult↗
PubMed1997

Use of protein A gene fusions for the analysis of structure-function relationship of the transactivator protein C of bacteriophage Mu.

A sensitive dimerization assay for DNA binding proteins has been developed using gene fusion technology. For this purpose, we have engineered a gene fusion using protein A gene of Staphylococcus aureus and C gene, the late gene transactivator of bacteriophage Mu. The C gene was fused to the 3' end of the gene for protein A to generate an A-C fusion. The overexpressed fusion protein was purified in a single step using immunoglobulin affinity chromatography. Purified fusion protein exhibits DNA binding activity as demonstrated by electrophoretic mobility shift assays. When the fusion protein A-C was mixed with C and analyzed for DNA binding, in addition to C and A-C specific complexes, a single intermediate complex comprising of a heterodimer of C and A-C fusion proteins was observed. Further, the protein A moiety in the fusion protein A-C does not contribute to DNA binding as demonstrated by proteolytic cleavage and circular dichroism (CD) analysis. The assay has also been applied to analyze the DNA binding domain of C protein by generating fusions between protein A and N- and C-terminal deletion mutants of C. The results indicate a role for the region towards the carboxy terminal of the protein in DNA binding. The general applicability of this method is discussed.

Amino Acid Sequence↗
PubMed1997

Breeding of bonnet monkeys (Macaca radiata) in captivity.

The results of studies on the breeding of South Indian bonnet monkeys (macaca radiata) over 20 years at our institution are presented. The menstrual cycle and hormonal changes were similar to those reported for Macaca mulatta. It was noted that summer amenorrhoea could be eliminated by housing the monkeys in rooms supplied with humidified air. Although a fertility index (proportion of animals becoming pregnant within three exposures to a proven fertile male) of 60 to 65% was achieved by random breeding, an index of 80 to 85% was achieved by controlled breeding (prior monitoring of serum estradiol-17 beta concentration on days 7, 8, 9, and 10).

Amenorrhea↗
PubMed1997

Expression of NF2-encoded merlin and related ERM family proteins in the human central nervous system.

Germline mutations of the neurofibromatosis 2 (NF2) gene are associated with an increased incidence of gliomas and glial harmartomas, suggesting a role for the NF2-encoded protein, merlin, in glial growth control. Using monoclonal and polyclonal anti-merlin antibodies for Western blotting and immunohistochemistry, we evaluated the cellular pattern of merlin expression in the normal human central nervous system (CNS), reactive gliosis; and NF2-associated glial hamartomas. In the normal CNS, merlin is widely expressed in coarse cytoplasmic granules in both glia and neurons, with less pronounced expression in other cells. Merlin is also expressed in reactive astrocytes and in the astrocytes of NF2-associated glial hamartomas. In reactive astrocytes, however, merlin is also present at the cell membrane and in cellular processes, suggesting redistribution of the protein in activated cells. Merlin is structurally related to ezrin, radixin and moesin, which are also expressed in the CNS, as demonstrated by Western blotting. The pattern of merlin expression, however, is distinct from that of ezrin, which has been previously described, and that of moesin, in which immunohistochemistry with an anti-moesin antibody showed expression in endothelial cells, glia and neurons in a membranous or diffuse cytoplasmic pattern. These findings imply that merlin has widespread and specific functions in the human central nervous system.

Adult↗
PubMed1997

Domiciliary health counselling in patients with sexually transmitted diseases.

To improve treatment compliance, follow-up and attendance of STD patients and their contacts, a programme, based on domiciliary visits was attempted. The programme was limited to male defaulters not responding to written and telephone calls. House visits to 79 out of 169 defaulters were made. Approximately half the number of houses were found locked. Fourteen defaulting patients reported for completion of their treatment and follow-up. Of these 11 were directly interviewed. None of the 14 patients agreed to disclose the addresses of their extramarital partners. During the study period 51 female sex contacts reported for treatment as compared to 27 in the control group. Though the numbers were small the study revealed that direct contact with the patient yielded the best results. It is suggested that to make the system cost-effective the health workers should spend time with STD patients in the clinic to mark out the correct location and time for meeting the patient either in the work place or at home in case of a follow-up.

Aftercare↗
PubMed1997

Tuberculoma of the tongue presenting as macroglossia.

Lingual tuberculosis presenting as macroglossia in a 20-year-old woman has been reported. The histopathologic picture was similar to lupus vulgaris and the intradermal tuberculin test showed a strongly positive vesiculobullous reaction after forty-eight hours. No active internal focus of tubercular infection could be detected. The patient responded well to antituberculous chemotherapy. The relative lack of symptoms suggest that the enlargement had been a slow process resulting from the lodging of bacilli in the tongue.

Adult↗
PubMed1997

Universal absence of merlin, but not other ERM family members, in schwannomas.

NF2 (neurofibromatosis 2, encoding the merlin protein) gene mutations and chromosome 22q loss have been demonstrated in the majority of sporadic and NF2-associated schwannomas, but many schwannomas fail to demonstrate genetic evidence of biallelic NF2 gene inactivation. In addition, the role of the merlin-related ERM family members (ezrin, radixin, and moesin) remains unclear in these tumors. We therefore studied expression of NF2-encoded merlin as well as ezrin, radixin, and moesin in 22 vestibular and peripheral schwannomas that had been evaluated for NF2 mutations and chromosome 22q loss. Western blotting and immunohistochemistry with antibodies directed against the amino and carboxy termini of merlin demonstrated loss of merlin expression in all studied schwannomas, including 12 tumors lacking genetic evidence of biallelic NF2 gene inactivation. Western blotting with antibodies directed against ezrin, radixin, and moesin, however, showed expression of these proteins in all schwannomas. In addition, immunohistochemistry with an antibody to moesin revealed widespread expression in tumor and endothelial cells. These data indicate that the specific loss of merlin is universal to schwannomas and is not linked to loss of ezrin, radixin, or moesin expression.

Blood Proteins↗
PubMed1997

Intragenic suppression in tRNA: evidence for crosstalk between the D and the T stems.

We showed previously that introduction of two of the three unique features of Escherichia coli initiator tRNA onto an elongator methionine tRNA conferred significant activity in initiation. Surprisingly, introduction also of the third unique feature, the A11:U24 base pair in the D stem, resulted in total lack of accumulation of the mutant Mi:3 tRNA. We show here that the Mi:3 tRNA gene is transcribed efficiently in vitro. Processing of the Mi:3 precursor transcript shows, however, that both the precursor and the mature Mi:3 tRNA are unstable in E. coli extracts. To understand the basis of instability caused by the A11:U24 base pair in the elongator methionine tRNA background, we have isolated and characterized intragenic suppressor mutations in the tRNA that restore its function in translation initiation. Sequence changes in the T stem that convert the existing A51 x C63 mismatch to a base pair in the Mi:3 tRNA result in accumulation of the tRNAs in vivo. The initiation activity and in vivo levels of accumulation of these suppressors are in the order Mi:3/G51:C63 > Mi:3/A51:U63 >> Mi:3/G51.U63. These results show that the in vivo accumulation of a tRNA with A11:U24 base pair in the D stem depends upon a base pair between positions 51 and 63 in the T stem. Structural analysis in vitro of the Mi:3 and Mi:3/G51:C63 transcripts suggests that the Mi:3 tRNA is unable to adopt a stable tRNA-like conformation. Various considerations suggest that this is most likely due to a high entropic barrier to tertiary interactions, between the D and the T loops necessary for the formation of a stable tRNA structure.

Base Sequence↗
PubMed1996

The merlin tumor suppressor localizes preferentially in membrane ruffles.

Merlin is a tumor suppressor whose inactivation underlies the familial schwannomas and meningiomas of neurofibromatosis 2 and their sporadic counterparts. It bears striking similarity to the ERM proteins, ezrin, radixin and moesin, members of the protein 4.1 superfamily that link proteins in the cytoskeleton and the plasma membrane. We have generated polyclonal and monoclonal antibodies that detect merlin as an approximately 66 kD protein in many different cell types. Using indirect immunofluorescence we have for the first time visualized endogenous merlin and localized it to the motile regions, such as leading or ruffling edges, in human fibroblast and meningioma cells. Merlin co-localizes with F-actin in these motile regions but is not associated with stress fibers. Merlin does not localize to the same structures as either ezrin or moesin in human meningioma cells, suggesting a function distinct from these ERMs. Thus, merlin is associated with motile regions of the cell and its participation in these structures may be intimately involved in control of proliferation in Schwann cells and meningeal cells.

Actins↗
PubMed1996

Cloning and characterization of a novel human clathrin heavy chain gene (CLTCL).

An exon representing a novel clathrin heavy chain gene (CLTCL) was isolated during gene identification studies and transcription mapping of human chromosome 22. Isolation and sequencing of cDNA clones corresponding to this exon revealed extensive similarity of the predicted amino acid sequence of this gene product to those of clathrin heavy chain genes of other species. Northern blot analysis has revealed an apparent developmental expression pattern of an approximately 6-kb mRNA. The gene appears to be expressed ubiquitously in the limited number of fetal tissues that were tested, but is selectively expressed in certain adult tissues, particularly in skeletal muscle. In addition, alternative splicing of an exon was observed near the carboxyl terminus of the predicted gene product. Its location overlaps the domain putatively involved in clathrin light chain binding and is adjacent to the heavy chain self-assembly (or trimerization) region, suggesting that alternative splicing may be involved in regulating one or both of these interactions. The expression pattern of this gene, in addition to its potential role in receptor-mediated endocytosis and signal transduction, suggests that it may be important in some developmental processes. The location of CLTCL on human chromosome 22 near the region commonly deleted in DiGeorge and other apparent haploinsufficiency syndromes warrants further investigation into its relationship with these developmental disorders.

Adult↗
PubMed1996

Sequence-specific DNA binding of the phage Mu C protein: footprinting analysis reveals altered DNA conformation upon protein binding.

The mom gene of bacteriophage Mu, which codes for a DNA modification function, is regulated in a complex manner at both transcriptional and translational levels. The phage-encoded C protein functions as an activator of mom transcription. The mom promoter has features of an activator-dependent weak promoter, and the C binding site is located upstream and overlapping the -35 region and includes the palindromic sequence TTAT(N)6ATAA. The interactions of this activator protein at its binding site in Pmom has been investigated using four different chemical footprinting reagents. The protein footprint spans a region of 18 to 25 bp, depending on the nature of the chemical reagent used. Dimethylsulfate protection experiments revealed the base-specific interactions. The protected guanines are separated by 15 bp and are located beyond the interrupted palindromic sequence. A tripartite footprint was observed with hydroxyl radical, generated by Fe(II)-EDTA, which shows the binding of the protein to one face of the helix. The extent of protection conferred by the bound protein, however, is not uniform, suggesting that the interaction is asymmetric. The chemical nuclease 1,10-phenanthroline-copper, a minor groove specific ligand, shows hyper-reactivity upon protein binding in the top strand nucleotide triplet CAC, again confirming the protein-induced alterations in DNA conformation. Gel exclusion chromatography and chemical crosslinking experiment with the purified protein suggest that this mode of interaction is accomplished by a dimeric protein. This observation is supported by electrophoretic mobility shift assay using heterodimer of pure C protein and staphylococcal protein A-C fusion. The deletion analysis implicates a role for the carboxyl-terminal region of the protein in DNA binding.

Base Sequence↗
PubMed1996

1H-NMR characterization of L-tryptophan binding to TRAP, the trp RNA-binding attenuation protein of Bacillus subtilis.

A 1H-NMR study of the binding of L-tryptophan to the trp RNA-binding attenuation protein of Bacillus subtilis (TRAP), an ondecamer (91.6 kDa), has been implemented. The assignment of the aromatic indole ring proton resonances of the bound tryptophan ligand has been successfully carried out by two-dimensional chemical exchange experiments. The observation of only a single set of chemical shifts of the bound ligand demonstrates that the tryptophan binding site is identical in all the 11 subunits of the protein. Further, the large change in ligand chemical shifts suggests that the conformation of tryptophan ligand undergoes a significant rearrangement after complex formation with TRAP. This is further substantiated by the extensive ligand-induced chemical shift changes observed to the protein resonances and identification of several strong ligand-protein intermolecular nuclear Overhauser effects. A correlation of these preliminary NMR data with the X-ray crystal structure of the TRAP-tryptophan complex also suggests, tentatively, that the observed changes to the NMR spectra of the protein might correspond to changes associated with residues surrounding the tryptophan binding pocket owing to complex formation.

Bacillus subtilis↗
PubMed1996

NMR studies of the mode of binding of corepressors and inducers to Escherichia coli trp repressor.

The binding of the corepressors tryptophan and 5-methyltryptophan and of the inducers 3-indolepropionate, 3-indoleacrylate and 5-methylindole to the Escherichia coli trp repressor have been studied by 1H-NMR spectroscopy. Identification of the resonances of the protons of bound ligands and their NOEs to protons of the protein (measured as transferred NOE) was greatly facilitated by the use of samples of the protein in which the hydrogens of all residues except alanine, isoleucine and threonine was replaced by deuterium. Chemical-shift changes of protein-backbone resonances and side-chain-amide resonances on ligand binding were measured with generally or selectively 15N-labelled protein. The patterns of changes in the chemical shifts of protein resonances and, particularly, ligand resonances distinguish the corepressors from the inducers, indicating, in agreement with earlier work, that corepressors and inducers bind to the protein in different ways. The NOEs observed for the bond ligands have been used to determine the position of the ligands in the crystallographically determined binding site, by means of a simulated-annealing molecular-dynamics protocol. The structures obtained show that the orientation in the binding site of the indole rings of tryptophan and 5-methyltryptophan and of 3-indolepropionate and 3-indoleacrylate differ by approximately 180 degrees in solution (in agreement with the crystallographic data for complexes of the trp repressor with tryptophan or with 3-indolepropionate). The value and limitations of calculating ligand positions based on transferred NOE are discussed.

Bacterial Proteins↗
PubMed1996

Frequency and distribution of NF2 mutations in schwannomas.

Sporadic and inherited schwannomas were scanned for the nature, frequency, and distribution of mutations in the NF2 locus encoding the merlin tumor suppressor protein on 22q. Of 58 tumors, 47% displayed loss of heterozygosity for NF2, leaving a total of 89 NF2 alleles to be examined. Pathogenic alterations were identified in 62 of these alleles, including 36 frameshifts with premature termination, 14 nonsense mutations, and 12 changes presumed to affect splicing. Effects of ten of the latter were confirmed in the NF2 transcript and indicated that activation of cryptic splice sites in coding sequence is another frequent mechanism leading to truncation of merlin. The mutations were relatively evenly distributed across both the protein 4.1 superfamily (exons 1-9) and the alpha-helical (exons 10-15) domains of merlin, but they did not occur at all in exons 16 and 17, which encode the protein's alternative COOH-termini. The data support the "two-hit" tumor suppressor model for formation of schwannomas and indicate that loss of merlin function can be achieved by truncation at various locations in the protein. However, the absence of mutations in exons 16 and 17 suggests that an inactivating mutation affecting only one of the merlin's alternative termini may not be sufficient to eliminate tumor suppressor function.

Adult↗
PubMed1996

Neurofibromatosis 2: loss of merlin's protective spell.

Schwannomas and meningiomas occur as multiple tumors in sufferers of neurofibromatosis 2 (NF2) and as solitary tumors in the general population due to the inactivation of a gene at chromosome 22q12. In 1993, a location cloning approach revealed this tumor suppressor, dubbed merlin, as a novel member of a family of proteins that link elements of the cytoskeleton and the cell membrane. Subsequent investigations have confirmed merlin's role in tumor formation, but have yet to reveal its mechanism of action.

Animals↗