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N Ganesh

Publications and source records attributed to N Ganesh.

10 recordsLinked to original sources
PubMed2005

A multicenter phase II study of gemcitabine, paclitaxel, and cisplatin in chemonaïve advanced ovarian cancer.

OBJECTIVES: The objectives of this multicenter phase II study were to evaluate the effects of gemcitabine-paclitaxel-cisplatin combination chemotherapy on response rate, survival, and toxicity in patients with advanced epithelial ovarian cancer (AEOC). METHODS: Chemonaive AEOC patients with bidimensionally measurable disease or an elevated serum cancer antigen 125 level received cisplatin (70 mg/m(2)) on day 1 and paclitaxel (80 mg/m(2)) and gemcitabine (1000 mg/m(2)) on days 1 and 8, every 3 weeks. RESULTS: Between October 2000 and September 2001, 46 patients were enrolled. Sixteen patients underwent debulking surgery prior to chemotherapy. In 45 evaluable patients, overall response rate was 64.4% (7 CR and 22 PR). Median time-to-progression was 13.4 months (95% CI, 9.6-17.4 months); median progression-free survival was 12.3 months (95% CI, 8.8-15.6 months); median overall survival was 26.0 months (95% CI, 18 months-not reached); and 1-year survival was 74% (95% CI, 60-88%). The relative dose intensities of gemcitabine, paclitaxel, and cisplatin were 81.4%, 80.2%, and 89.8%, respectively. Grade 3/4 neutropenia was the predominant hematologic toxicity observed (73.9% of patients) followed by grade 3/4 leukopenia (56.5%), anemia (45.7%), thrombocytopenia (23.9%), and febrile neutropenia/neutropenic sepsis (26.1%). The predominant grade 3 nonhematologic toxicities were alopecia (43.5%) and diarrhea (19.6%). Grade 4 nonhematologic toxicities were nausea/vomiting, constipation, and uremia (2.2% each). Two treatment-related deaths occurred (neutropenic sepsis and uremia). CONCLUSION: Gemcitabine-paclitaxel-cisplatin combination chemotherapy is active with manageable toxicity in chemonaive patients with advanced ovarian cancer and should be explored in larger phase III trials.

Adult↗
PubMed2003

Mycobacterium smegmatis RecA protein is structurally similar to but functionally distinct from Mycobacterium tuberculosis RecA.

In eubacteria, RecA proteins belong to a large superfamily of evolutionarily conserved, filament-forming, functional homologs of DNA strand exchange proteins. Here, we report the functional characterization of Mycobacterium smegmatis (Ms) and Mycobacterium tuberculosis (Mt) RecA proteins. Although in some respects Ms and Mt RecA proteins are structural and functional homologs of Escherichia coli (Ec) RecA, there are significant differences as well. The single-stranded DNA-binding property of RecA proteins was analyzed by electrophoretic mobility shift assays. We observed that Ms or Mt RecA proteins bound single-stranded DNA in a manner distinct from that of Ec RecA: The former two were able to form protein-DNA complexes in the presence of high salt. Further experiments indicated that Ms or Mt RecA proteins catalyzed adenosine triphosphate hydrolysis at approximately comparable rates across a wide range of pHs. Significantly, DNA strand invasion promoted by Ms or Mt RecA proteins displayed similar kinetics but distinctly different pH profiles. In contrast to MtRecA, MsRecA by itself was unable to form joint molecules across a wide range of pHs. However, regardless of the order in which SSB was added, it was able to stimulate MsRecA to form joint molecules within a narrow pH range, indicating that SSB is a required accessory factor. Together, these results provide a source of sharp contrast between EcRecA and mycobacterial RecAs on the one hand and Mt and Ms RecA proteins on the other.

Adenosine Triphosphate↗
PubMed2003

Characterization of DNA strand transfer promoted by Mycobacterium smegmatis RecA reveals functional diversity with Mycobacterium tuberculosis RecA.

The RecA-like proteins constitute a group of DNA strand transfer proteins ubiquitous in eubacteria, eukarya, and archaea. However, the functional relationship among RecA proteins is poorly understood. For instance, Mycobacterium tuberculosis RecA is synthesized as a large precursor, which undergoes an unusual protein-splicing reaction to generate an active form. Whereas the precursor was inactive, the active form promoted DNA strand transfer less efficiently compared to EcRecA. Furthermore, gene disruption studies have indicated that the frequencies of allele exchange are relatively lower in Mycobacterium tuberculosis compared to Mycobacterium smegmatis. The mechanistic basis and the factors that contribute to differences in allele exchange remain to be understood. Here, we show that the extent of DNA strand transfer promoted by the M. smegmatis RecA in vitro differs significantly from that of M. tuberculosis RecA. Importantly, M. smegmatis RecA by itself was unable to promote strand transfer, but cognate or noncognate SSBs rendered it efficient even when added prior to RecA. In the presence of SSB, MsRecA or MtRecA catalyzed strand transfer between ssDNA and varying lengths of linear duplex DNA with distinctly different pH profiles. The factors that were able to suppress the formation of DNA networks greatly stimulated strand transfer reactions promoted by MsRecA or MtRecA. Although the rate and pH profiles of dATP hydrolysis catalyzed by MtRecA and MsRecA were similar, only MsRecA was able to couple dATP hydrolysis to DNA strand transfer. Together, these results provide insights into the functional diversity in DNA strand transfer promoted by RecA proteins of pathogenic and nonpathogenic species of mycobacteria.

Adenosine Triphosphate↗
PubMed2003

Structural studies on MtRecA-nucleotide complexes: insights into DNA and nucleotide binding and the structural signature of NTP recognition.

RecA protein plays a crucial role in homologous recombination and repair of DNA. Central to all activities of RecA is its binding to Mg(+2)-ATP. The active form of the protein is a helical nucleoprotein filament containing the nucleotide cofactor and single-stranded DNA. The stability and structure of the helical nucleoprotein filament formed by RecA are modulated by nucleotide cofactors. Here we report crystal structures of a MtRecA-ADP complex, complexes with ATPgammaS in the presence and absence of magnesium as well as a complex with dATP and Mg+2. Comparison with the recently solved crystal structures of the apo form as well as a complex with ADP-AlF4 confirms an expansion of the P-loop region in MtRecA, compared to its homologue in Escherichia coli, correlating with the reduced affinity of MtRecA for ATP. The ligand bound structures reveal subtle variations in nucleotide conformations among different nucleotides that serve in maintaining the network of interactions crucial for nucleotide binding. The nucleotide binding site itself, however, remains relatively unchanged. The analysis also reveals that ATPgammaS rather than ADP-AlF4 is structurally a better mimic of ATP. From among the complexed structures, a definition for the two DNA-binding loops L1 and L2 has clearly emerged for the first time and provides a basis to understand DNA binding by RecA. The structural information obtained from these complexes correlates well with the extensive biochemical data on mutants available in the literature, contributing to an understanding of the role of individual residues in the nucleotide binding pocket, at the molecular level. Modeling studies on the mutants again point to the relative rigidity of the nucleotide binding site. Comparison with other NTP binding proteins reveals many commonalties in modes of binding by diverse members in the structural family, contributing to our understanding of the structural signature of NTP recognition.

Adenosine Diphosphate↗
PubMed2003

Crystal structures of Mycobacterium smegmatis RecA and its nucleotide complexes.

The crystal structures of Mycobacterium smegmatis RecA (RecA(Ms)) and its complexes with ADP, ATPgammaS, and dATP show that RecA(Ms) has an expanded binding site like that in Mycobacterium tuberculosis RecA, although there are small differences between the proteins in their modes of nucleotide binding. Nucleotide binding is invariably accompanied by the movement of Gln 196, which appears to provide the trigger for transmitting the effect of nucleotide binding to the DNA-binding loops. These observations provide a framework for exploring the known properties of the RecA proteins.

Adenosine Diphosphate↗
PubMed2002

RecX protein abrogates ATP hydrolysis and strand exchange promoted by RecA: insights into negative regulation of homologous recombination.

In many eubacteria, coexpression of recX with recA is essential for attenuation of the deleterious effects of recA overexpression; however, the molecular mechanism has remained enigmatic. Here, we show that Mycobacterium tuberculosis RecX binds directly to M. tuberculosis RecA as well as M. smegmatis and E. coli RecA proteins in vivo and in vitro, but not single-stranded DNA binding protein. The direct association of RecX with RecA failed to regulate the specificity or extent of binding of RecA either to DNA or ATP, ligands that are central to activation of its functions. Significantly, RecX severely impeded ATP hydrolysis and the generation of heteroduplex DNA promoted by homologous, as well as heterologous, RecA proteins. These findings reveal a mode of negative regulation of RecA, and imply that RecX might act as an anti-recombinase to quell inappropriate recombinational repair during normal DNA metabolism.

Adenosine Triphosphate↗
PubMed2001

Model for interacting instabilities and texture dynamics of patterns.

A simple model to study interacting instabilities and textures of resulting patterns for thermal convection is presented. The model, consisting of a twelve-mode dynamical system derived for periodic square lattice, describes convective patterns in the form of stripes and patchwork quilt. The interaction between stationary zigzag stripes and standing patchwork quilt pattern leads to spatiotemporal patterns of twisted patchwork quilt. Textures of these patterns, which depend strongly on Prandtl number, are investigated numerically using the model. The model also shows an interesting possibility of a multicritical point, where stability boundaries of four different structures meet.

Journal Article↗
PubMed2000

Crystal structures of Mycobacterium tuberculosis RecA and its complex with ADP-AlF(4): implications for decreased ATPase activity and molecular aggregation.

Sequencing of the complete genome of Mycobacterium tuberculosis, combined with the rapidly increasing need to improve tuberculosis management through better drugs and vaccines, has initiated extensive research on several key proteins from the pathogen. RecA, a ubiquitous multifunctional protein, is a key component of the processes of homologous genetic recombination and DNA repair. Structural knowledge of MtRecA is imperative for a full understanding of both these activities and any ensuing application. The crystal structure of MtRecA, presented here, has six molecules in the unit cell forming a 6(1) helical filament with a deep groove capable of binding DNA. The observed weakening in the higher order aggregation of filaments into bundles may have implications for recombination in mycobacteria. The structure of the complex reveals the atomic interactions of ADP-AlF(4), an ATP analogue, with the P-loop-containing binding pocket. The structures explain reduced levels of interactions of MtRecA with ATP, despite sharing the same fold, topology and high sequence similarity with EcRecA. The formation of a helical filament with a deep groove appears to be an inherent property of MtRecA. The histidine in loop L1 appears to be positioned appropriately for DNA interaction.

Adenosine Diphosphate↗
PubMedDate not supplied

Prevalence of neurosyphilis at Government Rajaji Hospital, Madurai, India.

Forty patients (34 males and 6 females) with neurological complaints/manifestations and with a past history of multiple sexual partners attending the Government Rajaji Hospital, Madurai, India between April 1992 and October 1992 were investigated for neurosyphilis. Metabolic disorders, hypertension, ischaemic heart disease, arrhythmias and trauma were excluded. Seven males (17.5%) were found to have neurosyphilis. The youngest was 26 years old and the oldest was 47. All were married and of low socioeconomic background. Meningovascular syphilis was the predominant presentation (6:1). Associated cardiovascular involvement was noticed in one of the cases. There was no associated HIV infection in these cases. The incidence is higher than previous reports from this centre.

Adult↗