Nucleic Acids Research, 1995, Vol. 23, No. 11 1887-1893
© 1995
MOLECULAR BIOLOGY |
Phosphorylation of the Oxytricha telomere protein: possible cell cycle regulation
1 Department of Molecular, Cellular and Developmental Biology USA 2 Department of Chemistry and Biochemistry, Howard Hughes Medical Institute University of Colorado, Boulder, CO 80309-0215, USA 3 Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine Denver, CO 80262, USA 4 Department of Biological Chemistry, School of Medicine, University of California Davis, CA 95016, USA 5 Life Sciences Division, Los Alamos National Laboratory Los Alamos, NM 87545, USA
* To whom correspondence should be addressed
Received March 3, 1995. Accepted April 18, 1995.
In the macronucleus of the ciliate Oxytricha nova, telomeres end with single-stranded (T4G4)2 DNA bound to a heterodimeric telomeVe protein (
β). Both the and β subunits (-TP and β-TP) were phosphory-lated in asynchronously growing Oxytricha; β-TP was phosphorylated to a much higher degree. In vitro, mouse cyclIn-dependent kineses (Cdks) phosphory-lated β-TP In a lyslne-rlch domain that Is not required for specific DNA binding but is implicated in higher order structure formation of telomeres. Therefore, phosphorylation of β-TP could modulate a function of the telomere protein that is separate from specific DNA binding. Phosphoamino acid analysis revealed that the mouse Cdks modify predominantly threonlne residues in β-TP, consistent with the observation that β-TP contains two consensus Cdk recognition sequences containing threonlne residues. In Xenopus egg extracts that undergo cell cycling, β-TP was phos-phorylated In M phase and dephosphorylated In interphase. This work provides the first direct evidence of phosphorylation at telomeres in any organism, as well as indirect evidence for cell cycle regulation of telomere phosphorylation. The Cdc2/cyclin A and Cdc2/cyclin B kinases are required for major m It otic events. An attractive model is that phosphorylation of β-TP by these kinases is required for the breakdown of telomere associations with each other and/or with nuclear structures prior to nuclear division.
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