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Mitsunobu, Hitoshi

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Mitsunobu

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Hitoshi

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Mitsunobu, Hitoshi
Author's Publications: search.filters.isAuthorOfPublication.3c07f9e6-6b82-4d8a-95c4-227de1bb8248

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    Roles of Piwi Proteins in Transcriptional Regulation Mediated by HP1s in Cultured Silkworm Cells
    (Public Library of Science, 2014) Tatsuke, Tsuneyuki; Li, Zhiqing; Zhu, Li; Mitsunobu, Hitoshi; Yoshimura, Kaito; Mon, Hiroaki; Lee, Jae Man; Kusakabe, Takahiro
    Piwi proteins are part of a superfamily of Argonaute proteins, which are one of the core components of the RNA silencing pathway in many eukaryotes. Piwi proteins are thought to repress the transposon expression both transcriptionally and post-transcriptionally. Recently, Drosophila melanogaster Piwi was recently reported to associate with chromatin and to interact directly with the Heterochromatin Protein 1 (HP1a). However, similar interactions have not been reported in other higher eukaryotes. Here we show that silkworm Piwi proteins interact with HP1s in the nucleus. The silkworm, Bombyx mori, has two Piwi proteins, Ago3 and Siwi, and two typical HP1 proteins, HP1a and HP1b. We found that HP1a plays an important role in the interaction between Ago3/Siwi and HP1b in the ovary-derived BmN4 cell line. We also found that Ago3/Siwi regulates the transcription in an HP1-dependent manner. These results suggest that silkworm Piwi proteins function as a chromatin regulator in collaboration with HP1a and HP1b.
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    Flap endonuclease of bacteriophage T7: Possible roles in RNA primer removal, recombination and host DNA breakdown
    (Landes Bioscience, 2014) Mitsunobu, Hitoshi; Zhu, Bin; Lee, Seung-Joo; Tabor, Stanley; Richardson, Charles
    Gene 6 protein of bacteriophage T7 has 5′-3′-exonuclease activity specific for duplex DNA. We have found that gene 6 protein also has flap endonuclease activity. The flap endonuclease activity is considerably weaker than the exonuclease activity. Unlike the human homolog of gene 6 protein, the flap endonuclease activity of gene 6 protein is dependent on the length of the 5′-flap. This dependency of activity on the length of the 5′-flap may result from the structured helical gateway region of gene 6 protein which differs from that of human flap endonuclease 1. The flap endonuclease activity provides a mechanism by which RNA-terminated Okazaki fragments, displaced by the lagging strand DNA polymerase, are processed. 3′-extensions generated during degradation of duplex DNA by the exonuclease activity of gene 6 protein are inhibitory to further degradation of the 5′-terminus by the exonuclease activity of gene 6 protein. The single-stranded DNA binding protein of T7 overcomes this inhibition.