Articles written in Journal of Biosciences

    • Comparative analysis of prosomes and multicatalytic proteinases from rabbit erythrocytes

      Jayanta K Pal Koko Murakami

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      Prosomes and multicatalytic proteinases were purified from rabbit erythrocyte lysates and were analysed to determine their relationship. During purification by sucrose density gradient centrifugation using low salt buffer, they sedimented at 20–26S. Upon further purification, using high salt buffer, prosomes were recovered as 20S complexes as determined by their characteristic polypeptide pattern. Interestingly, both the 26S and 20S components had protease activity. Therefore, in order to determine their relationship with the multicatalytic proteinases, which are reported to contain a similar set of polypeptides, highly pure prosomes and the multicatalytic proteinases were analysed. Both 20S prosomes and multicatalytic proteinases showed protease activity and also had identical protein subunits of molecular weight ranging from 21 kDa to 35 kDa. Among these, at least two were immunologically identical as determined by Western blot using two monoclonal antibodies prepared against duck prosomes. Furthermore, protease activities of both components were inhibited almost to the same extent by an endogenous inhibitor specific for high molecular weight proteases and calpain. These results thus establish that the 20S prosomes and multicatalytic proteinases are identical, and suggest further that proteolytic activity could be the principal function of prosomes.

    • Hsp90 regulates protein synthesis by activating the heme-regulated eukaryotic initiation factor 2α (eIF-2α) kinase in rabbit reticulocyte lysates

      Jayanta K Pal

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      Heat shock protein 90 (Hsp90), an abundant and ubiquitous cytoplasmic protein has recently been indicated to participate in the regulation of protein synthesis by interacting with the heme-regulated eukaryotic initiation factor 2α (eIF-2α) kinase, also known as the heme-regulated inhibitor (HRI). However, there exists an ambiguity on the exact nature of its action. In this investigation, the interaction of Hsp90 and HRI has been examined bothin vitro using purified proteins, andin situ in rabbit reticulocyte lysates subjected to heat shock and treatment with N-ethylmaleimide (NEM), a sulfhydryl reagent known to induce stress response. During heat shock or NEM-treatment of reticulocyte lysates, Hsp90 co-immunoprecipitated with activated HRI by anti-HRI monoclonal antibodies. Furthermore, the amount of Hsp90 being associated with HRI was a function of duration of heat shock and was correlated with the extent of HRI activation. Interestingly, simultaneous heat shock and NRM-treatment of reticulocyte lysates led to maximal association of HRI and Hsp90, leaving nearly no free HRI in the lysates.In vitro, with the purified proteins, the autokinase and the eIF-2α kinase activities of HRI were enhanced when HRI was pre-incubated with Hsp90, both in the presence and absence of hemin. These data, therefore, clearly demonstrate that Hsp90 interacts with HRI during stress, and that this association leads to activation of HRI and thereby inhibition of protein synthesis at the level of initiation. Considering the ubiquitous nature of Hsp90 and the presence of HRI or HRI-like eIF-2α kinase activity in a number of organisms, it is highly possible that Hsp90 may universally mediate down regulation of global protein synthesis during stress response.

    • Untranslated regions of mRNA and their role in regulation of gene expression in protozoan parasites


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      Protozoan parasites are one of the oldest living entities in this world that throughout their existence have shown excellentresilience to the odds of survival and have adapted beautifully to ever changing rigors of the environment. In view of thedynamic environment encountered by them throughout their life cycle, and in establishing pathogenesis, it is unsurprisingthat modulation of gene expression plays a fundamental role in their survival. In higher eukaryotes, untranslated regions(UTRs) of transcripts are one of the crucial regulators of gene expression (influencing mRNA stability and translationefficiency). Parasitic protozoan genome studies have led to the characterization (in silico, in vitro and in vivo) of a largenumber of their genes. Comparison of higher eukaryotic UTRs with parasitic protozoan UTRs reveals the existence ofseveral similar and dissimilar facets of the UTRs. This review focuses on the elements of UTRs of medically importantprotozoan parasites and their regulatory role in gene expression. Such information may be useful to researchers in designinggene targeting strategies linked with perturbation of host-parasite relationships leading to control of specific parasites.

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