• RAJANI KANT CHITTELA

      Articles written in Journal of Biosciences

    • Translin: A multifunctional protein involved in nucleic acid metabolism

      ALKA GUPTA VINAYAKI S PILLAI RAJANI KANT CHITTELA

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      Translin, a highly conserved, DNA/RNA binding protein, is abundantly expressed in brain, testis and in certain malignancies.It was discovered initially in the quest to find proteins that bind to alternating polypurines-polypyrimidines repeats.It has been implicated to have a role in RNA metabolism (tRNA processing, RNAi, RNA transport, etc.), transcription,DNA damage response, etc. Studies from human, mice, drosophila and yeast have revealed that it forms an octameric ring,which is important for its function. Translin is a cytoplasmic protein, but under genotoxic stress, it migrates into thenucleus, binds to the break point hot spots and therefore, thought to be involved in chromosomal translocation events aswell as DNA damage related response. Its structure is known and DNA binding regions, GTP binding region and regionsresponsible for homotypic and heterotypic interaction are known. It forms a ball like structure with open central channel foraccommodating the substrate nucleic acids. Besides this, translin protein binds to 30 and 50 UTR of certain mRNAs andprobably regulates their availability for translation. It is also involved in mRNA transport and cell cycle progression. Itforms a heteromeric complex with translin associated factor-X (TRAX) to form C3PO complex which is involved in RNAsilencing process. Recently, it has been shown that translin is upregulated under starvation conditions in Drosophila and isinvolved in the integration of sleep and metabolic rate of the flies. Earlier studies classified translin as a DNA repair protein;however subsequent studies showed that it is a multifunctional protein. With this background, in this review we havesummarized the translin biochemical activities, cellular function as well as structural properties of this important protein.

    • Modulation of photosynthesis in Synechocystis and Synechococcus grown with chromium (VI)

      ALKA GUPTA JAYASHREE K SAINIS SURESH G BHAGWAT RAJANI KANT CHITTELA

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      Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942 exhibit dissimilar tolerance to Cr(VI) witha tenfold difference in their EC50 value for Cr(VI). This contrasting tolerance was attributed to the difference in theability to transport Cr(VI) and to detoxify ROS. The present study used biochemical assays and chlorophyllfluorescence to investigate the effect of growth with Cr(VI) on photosynthesis in the two cyanobacteria. Inabsence of Cr(VI), all the measured parameters viz., rates of CO2 fixation, PSII and PSI activities were higher inSynechocystis in comparison to Synechococcus, suggesting intrinsic differences in their photosynthesis. Growthin the presence of Cr(VI) reduced the pigment content and photosystems’ activities in both cyanobacteria. It wasfurther observed that photosynthetic functions were more adversely affected in Synechocystis in comparisonto Synechococcus, in spite of exposure to tenfold lower Cr(VI) concentration. The effective quantumyield of PSIIand PSI obtained by chlorophyll fluorescence measurements increased in the presence of Cr(VI) in Synechococcuswhereas it decreased in Synechocystis. However, the overall CO2 fixation remained unchanged. These resultsindicated that, in addition to the intrinsic difference in photosynthetic rates, the two cyanobacteria exhibit differentialmodulation of photosynthetic machinery upon Cr(VI) exposure and Synechococcus could adapt betterit’s photosystems to counter the oxidative stress.

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