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			PubMed Journals: Eur J Biochem

  Source:		PMID: 7635160


    		Eur J Biochem. 1995 Jul 15;231(2):491-7.
     
			Human topoisomerase II alpha is phosphorylated
			in a cell-cycle phase-dependent manner by
			a proline-directed kinase.

			Wells NJ(1), Hickson ID.

			Author Information
			(1) Imperial Cancer Research Fund Laboratories,
			Institute of Molecular Medicine,
			University of Oxford, John Radcliffe Hospital,
			England.

			Topoisomerase II is essential for chromosome
			condensation and segregation at mitosis
			in eukaryotic cells, but the mechanism of
			its regulation is not clearly understood.
			We have investigated whether or not the
			alpha isozyme of human topoisomerase II
			is phosphorylated in a cell-cycle phase-dependent
			manner. Two-dimensional tryptic phosphopeptide
			mapping revealed that several sites on HeLa
			topoisomerase II alpha protein were phosphorylated
			predominantly or exclusively during the
			G2 and M phases. To identify the protein
			kinases involved in this cell-cycle phase-specific
			phosphorylation, oligohistidine-tagged recombinant
			domains of the topoisomerase II alpha protein
			were expressed in Escherichia coli, purified
			by affinity chromatography and phosphorylated
			in vitro by different protein kinases.
			Phosphorylation of the C-terminal domain of the
			topoisomerase II alpha protein by the universal
			mitotic controller, p34cdc2, generated multiple
			tryptic phosphopeptides, many of which corresponded
			to the G2/M-phase-specific phosphorylation
			sites observed in vivo. The same phosphopeptides
			were obtained following phosphorylation
			of the C-terminal domain in vitro by the
			mitogen-activated protein kinase. Site-directed
			mutagenesis studies identified five of these
			sites of phosphorylation, each of which
			comprised a serine-proline motif. Our data
			implicate one or more proline-directed kinases
			in the cell-cycle-dependent regulation of
			topoisomerase II alpha enzyme activity in
			human cells.

			PMID: 7635160 [Indexed for MEDLINE]

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