• Sudha Bhattacharya

      Articles written in Journal of Biosciences

    • Expression ofMycobacterium tuberculosis genes inEscherichia coli

      Sudha Bhattacharya Satishn Ranadive Alok Bhattacharya

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      TwoEscherichia coli clones expressingMycobacterium tuberculosis antigens were isolated from a gene-bank in the plasmid vector pBR 325. ‘Western blot’ analysis revealed the presence of a unique protein band of molecular weight 68,000 and 38,000, respectively in cellextracts from each clone. The 68,000 dalton antigen was found to be expressed onEscherichia coli outer surface. Plasmid DNA from a third clone could confer leucine independence on two differentleu B mutants ofEscherichia coli but not on mutants in otherleu genes, pointing to the possibility ofgenetic complementation. Thus,Mycobacterium tuberculosis DNA is capable of expression inEscherichia coli.

    • Pathogenesis of infection byEntamoeba histolytica

      Devinder Sehgal Alok Bhattacharya Sudha Bhattacharya

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      Entamoeba histolytica, a protozoan parasite, is the etiologic agent of amoebiasis in humans. It exists in two forms—the trophozoite which is the active, dividing form, and the cyst which is dormant and can survive for prolonged periods outside the host. In most infected individuals the trophozoites exist as commensals. In a small percentage of infections, the trophozoites become invasive and penetrate the intestinal mucosa, causing ulcers. The trophozoites may reach other parts of the body—mainly liver, where they cause tissue necrosis, leading to lifethreatening abscesses. It is thought that pathogenesis of infection byEntamoeba histolytica is governed at several levels, chief among them are (i) adherence of trophozoite to the target cell, (ii) lysis of target cell, and (iii) phagocytosis of target cell. Several molecules which may be involved in these processes have been identified. A lectin inhibitable by galactose and N-acetyl-D-galactosamine is present on the trophozoite surface. This is implicated in adherence of trophozoite to the target cell. Various amoebic poreforming proteins are known, of which 5kDa protein (amoebapore) has been extensively studied. These can insert into the lipid bilayers of target cells, forming ion-channels. The phagocytic potential of trophozoites is directly linked to virulence as measured in animal models. Factors like association of bacteria with trophozoites also influence virulence. Thus, pathogenesis is determined by multiple factors and a unifying picture taking into account the relative contributions of each factor is sought. Recent technical advances, which includes the development of a transfection system to introduce genes into trophozoites, should help to understand the mechanism of pathogenesis in amoebiasis.

    • Close sequence identity between ribosomal DNA episomes of the non-pathogenicEntamoeba dispar and pathogenicEntamoeba histolytica

      Jaishree Paul Alok Bhattacharya Sudha Bhattacharya

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      Entamoeba dispar andEntamoeba histolytica are now recognized as two distinct species-the former being nonpathogenic to humans. We had earlier studied the organization of ribosomal RNA genes inE. histolytica. Here we report the analysis of ribosomal RNA genes inE. dispar. The rRNA genes ofE. dispar, like their counterpart inE. histolytica are located on a circular rDNA molecule. From restriction map analysis, the size ofE. dispar rDNA circle was estimated to be 24·4 kb. The size was also confirmed by linearizing the circle withBsaHI, and by limited DNAseI digestion. The restriction map of theE. dispar rDNA circle showed close similarity to EhR1, the rDNA circle ofE. histolytica strain HM-1:IMSS which has two rDNA units per circle. The various families of short tandem repeats found in the upstream and downstream intergenic spacers (IGS) of EhR1 were also present inE. dispar. Partial sequencing of the cloned fragments ofE. dispar rDNA and comparison with EhR1 revealed only 2·6% to 3·8% sequence divergence in the IGS. The region Tr and the adjoiningPvuI repeats in the IGS of EhR1, which are missing in thoseE. histolytica strains that have one rDNA unit per circle, were present in theE. dispar rDNA circle. Such close similarity in the overall organization and sequence of the IGS of rDNAs of two different species is uncommon. In fact the spacer sequences were only slightly more divergent than the 18S rRNA gene sequence which differs by 1·6% in the two species. The most divergent sequence betweenE. histolytica andE. dispar was the internal transcribed spacer, ITS2. Therefore, it was concluded that probes derived from the ITS1 and ITS 2 sequences would be more reliable and reproducible than probes from the IGS regions used earlier for identifying these species.

    • Identification of EhTIF-IA: The putative E. histolytica orthologue of the human ribosomal RNA transcription initiation factor-IA

      Ankita Srivastava Alok Bhattacharya Sudha Bhattacharya Gagan Deep Jhingan

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      Initiation of rDNA transcription requires the assembly of a specific multi-protein complex at the rDNA promoter containing the RNA Pol I with auxiliary factors. One of these factors is known as Rrn3P in yeast and Transcription Initiation Factor IA (TIF-IA) in mammals. Rrn3p/TIF-IA serves as a bridge between RNA Pol I and the pre-initiation complex at the promoter. It is phosphorylated at multiple sites and is involved in regulation of rDNA transcription in a growth-dependent manner. In the early branching parasitic protist Entamoeba histolytica, the rRNA genes are present exclusively on circular extra chromosomal plasmids. The protein factors involved in regulation of rDNA transcription in E. histolytica are not known. We have identified the E. histolytica equivalent of TIF-1A (EhTIF-IA) by homology search within the database and was further cloned and expressed. Immuno-localization studies showed that EhTIF-IA co-localized partially with fibrillarin in the peripherally localized nucleolus. EhTIF-IA was shown to interact with the RNA Pol I-specific subunit RPA12 both in vivo and in vitro. Mass spectroscopy data identified RNA Pol I-specific subunits and other nucleolar proteins to be the interacting partners of EhTIF-IA. Our study demonstrates for the first time a conserved putative RNA Pol I transcription factor TIF-IA in E. histolytica.

  • Journal of Biosciences | News

      Forthcoming Special issue.

    • To trigger further research on plant mitochondria, the Journal of Biosciences is bringing out a special issue titled "Plant Mitochondria: Properties and Interactions with Other Organelles".

      Plant mitochondria are quite distinct and have unique features, such as a cyanide-insensitive alternate pathway. They also interact with chloroplasts to optimize photosynthetic carbon assimilation.

      Submissions are welcome until 30 July 2023. The contributions can be original articles, short communications, reviews, or mini-reviews on any topic related to plant mitochondria.

      Authors can submit their articles online at https://www.editorialmanager.com/jbsc/default2.aspx

      Posted on April 12, 2023
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      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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