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  • 1.
    Chiruvella, Kishore K.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Rajaei, Naghmeh
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Jonna, Venkateswara Rao
    Hofer, Anders
    Åström, Stefan U.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Biochemical Characterization of Kat1: a Domesticated hAT-Transposase that Induces DNA Hairpin Formation and MAT-Switching2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 21671Article in journal (Refereed)
    Abstract [en]

    Kluyveromyces lactis hAT-transposase 1 (Kat1) generates hairpin-capped DNA double strand breaks leading to MAT-switching (MATa to MAT alpha). Using purified Kat1, we demonstrate the importance of terminal inverted repeats and subterminal repeats for its endonuclease activity. Kat1 promoted joining of the transposon end into a target DNA molecule in vitro, a biochemical feature that ties Kat1 to transposases. Gas-phase Electrophoretic Mobility Macromolecule analysis revealed that Kat1 can form hexamers when complexed with DNA. Kat1 point mutants were generated in conserved positions to explore structure-function relationships. Mutants of predicted catalytic residues abolished both DNA cleavage and strand-transfer. Interestingly, W576A predicted to be impaired for hairpin formation, was active for DNA cleavage and supported wild type levels of mating-type switching. In contrast, the conserved CXXH motif was critical for hairpin formation because Kat1 C402A/H405A completely blocked hairpinning and switching, but still generated nicks in the DNA. Mutations in the BED zinc-finger domain (C130A/C133A) resulted in an unspecific nuclease activity, presumably due to nonspecific DNA interaction. Kat1 mutants that were defective for cleavage in vitro were also defective for mating-type switching. Collectively, this study reveals Kat1 sharing extensive biochemical similarities with cut and paste transposons despite being domesticated and evolutionary diverged from active transposons.

  • 2. Paritala, Vikram
    et al.
    Chiruvella, Kishore K.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Sri Venkateswara University, India.
    Thammineni, Chakradhar
    Ghanta, Rama Gopal
    Mohammed, Arifullah
    Phytochemicals and antimicrobial potentials of mahogany family2015In: Revista Brasileira de Farmacognosia, ISSN 0102-695X, E-ISSN 1981-528X, Vol. 25, no 1, p. 61-83Article, review/survey (Refereed)
    Abstract [en]

    Drug resistance to human infectious diseases caused by pathogens lead to premature deaths through out the world. Plants are sources for wide variety of drugs used for treating various diseases. Systematic screening of medicinal plants for the search of new antimicrobial drug candidates that can inhibit the growth of pathogens or kill with no toxicity to host is being continued by many laboratories. Here we review the phytochemical investigations and biological activities of Meliaceae. The mahogany (Meliaceae) is family of timber trees with rich source for limonoids. So far, amongst the different members of Meliaceae, Azadirachta indica and Melia dubia have been identified as the potential plant systems possessing a vast array of biologically active compounds which are chemically diverse and structurally complex. Despite biological activities on different taxa of Meliaceae have been carried out, the information of antibacterial and antifungal activity is a meager with exception to Azadirachta indica. Together we provide new insights of Meliaceae members demonstrating as a potential source as antimicrobial agents using in vitro studies.

  • 3.
    Rajaei, Naghmeh
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Chiruvella, Kishore K.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Lin, Feng
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Åström, Stefan U.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Domesticated transposase Kat1 and its fossil imprints induce sexual differentiation in yeast2014In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 43, p. 15491-15496Article in journal (Refereed)
    Abstract [en]

    Transposable elements (TEs) have had a major influence on shaping both prokaryotic and eukaryotic genomes, largely through stochastic events following random or near-random insertions. In the mammalian immune system, the recombination activation genes1/2 (Rag1/2) recombinase has evolved from a transposase gene, demonstrating that TEs can be domesticated by the host. In this study, we uncovered a domesticated transposase, Kluyveromyces lactis hobo/Activator/Tam3 (hAT) transposase 1 (Kat1), operating at the fossil imprints of an ancient transposon, that catalyzes the differentiation of cell type. Kat1 induces mating-type switching from mating type a (MATa) to MATa in the yeast K. lactis. Kat1 activates switching by introducing two hairpin-capped DNA double-strand breaks (DSBs) in the MATa1-MATa2 intergenic region, as we demonstrate both in vivo and in vitro. The DSBs stimulate homologous recombination with the cryptic hidden MAT left alpha (HML alpha) locus resulting in a switch of the cell type. The sites where Kat1 acts in the MAT alpha locus most likely are ancient remnants of terminal inverted repeats from a long-lost TE. The KAT1 gene is annotated as a pseudogene because it contains two overlapping ORFs. We demonstrate that translation of full-length Kat1 requires a programmed -1 frameshift. The frameshift limited Kat1 activity, because restoring the zero frame causes switching to the MATa genotype. Kat1 also was transcriptionally activated by nutrient limitation via the transcription factor mating type switch 1 (Mts1). A phylogenetic analysis indicated that KAT1 was domesticated specifically in the Kluyveromyces clade of the budding yeasts. We conclude that Kat1 is a highly regulated transposase- derived endonuclease vital for sexual differentiation.

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