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Articles by K Hirai
Total Records ( 2 ) for K Hirai
  S Muramatsu , K Hirai , Y. S Tak , Y Kamimura and H. Araki

Eukaryotic chromosomal DNA replication requires cyclin-dependent kinase (CDK) activity. CDK phosphorylates two yeast replication proteins, Sld3 and Sld2, both of which bind to Dpb11 when phosphorylated. These phosphorylation-dependent interactions are essential and are the minimal requirements for CDK-dependent activation of DNA replication. However, how these interactions activate DNA replication has not been elucidated. Here, we show that CDK promotes the formation of a newly identified fragile complex, the preloading complex (pre-LC) containing DNA polymerase (Pol ), GINS, Sld2, and Dpb11. Formation of the pre-LC requires phosphorylation of Sld2 by CDK, but is independent of DNA replication, protein association with replication origins, and Dbf4-dependent Cdc7 kinase, which is also essential for the activation of DNA replication. We also demonstrate that Pol , GINS, Dpb11, and CDK-phosphorylated Sld2 form a complex in vitro. The genetic interactions between Pol , GINS, Sld2, and Dpb11 suggest further that they form an essential complex in cells. We propose that CDK regulates the initiation of DNA replication in budding yeast through formation of the pre-LC.

  K Hirai , H Kuroyanagi , Y Tatebayashi , Y Hayashi , K Hirabayashi Takahashi , K Saito , S Haga , T Uemura and S. Izumi

l-kynurenine 3-monooxygenase (KMO) is an NAD(P)H-dependent flavin monooxygenase that catalyses the hydroxylation of l-kynurenine to 3-hydroxykynurenine, and is localized as an oligomer in the mitochondrial outer membrane. In the human brain, KMO may play an important role in the formation of two neurotoxins, 3-hydroxykynurenine and quinolinic acid, both of which provoke severe neurodegenerative diseases. In mosquitos, it plays a role in the formation both of eye pigment and of an exflagellation-inducing factor (xanthurenic acid). Here, we present evidence that the C-terminal region of pig liver KMO plays a dual role. First, it is required for the enzymatic activity. Second, it functions as a mitochondrial targeting signal as seen in monoamine oxidase B (MAO B) or outer membrane cytochrome b5. The first role was shown by the comparison of the enzymatic activity of two mutants (C-terminally FLAG-tagged KMO and carboxyl-terminal truncation form, KMOC50) with that of the wild-type enzyme expressed in COS-7 cells. The second role was demonstrated with fluorescence microscopy by the comparison of the intracellular localization of the wild-type, three carboxyl-terminal truncated forms (C20, C30 and C50), C-terminally FLAG-tagged wild-type and a mutant KMO, where two arginine residues, Arg461-Arg462, were replaced with Ser residues.

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