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J. Biol. Chem., Vol. 279, Issue 13, 12812-12818, March 26, 2004

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Interaction of an Arabidopsis RNA-binding Protein with Plant Single-stranded Telomeric DNA Modulates Telomerase Activity^*

Chian Kwon and In Kwon Chung

From the Department of Biology, Molecular Aging Research Center, and Protein Network Research Center, Yonsei University, Seoul 120-749, Korea

Telomeres are the specialized structures at the end of linear chromosomes and terminate with a single-stranded 3' overhang of the G-rich strand. The primary role of telomeres is to protect chromosome ends from recombination and fusion and from being recognized as broken DNA ends. This protective function can be achieved through association with specific telomere-binding proteins. Although proteins that bind single-stranded G-rich overhang regulate telomere length and telomerase activity in mammals and lower eukaryotes, equivalent factors have yet to be identified in plants. Here we have identified proteins capable of interacting with the G-rich single-stranded telomeric repeat from the Arabidopsis extracts by affinity chromatography. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis indicates that the isolated protein is a chloroplast RNA-binding protein (and a truncated derivative). The truncated derivative, which we refer to as STEP1 (single-stranded telomere-binding protein 1), binds specifically the single-stranded G-rich plant telomeric DNA sequences but not double-stranded telomeric DNA. Unlike the chloroplast-localized full-length RNA-binding protein, STEP1 localizes exclusively to the nucleus, suggesting that it plays a role in plant telomere biogenesis. We also demonstrated that the specific binding of STEP1 to single-stranded telomeric DNA inhibits telomerase-mediated telomere extension. The evidence presented here suggests that STEP1 is a telomere-end binding protein that may contribute to telomere length regulation by capping the ends of chromosomes and thereby repressing telomerase activity in plants.

Received for publication, November 3, 2003 , and in revised form, December 24, 2003.

^* This work was supported by Grant 02-PJ10-PG6-AG01-0010 from the Ministry of Health and Welfare, Korea, through the Molecular Aging Research Center and a grant from the Korea Science and Engineering Foundation through the Protein Network Research Center. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Biology, College of Science, Yonsei University, 134 Shinchon-dong, Seoul 120-749, Korea. Tel.: 822-2123-2660; Fax: 822-364-8660; E-mail: topoviro{at}yonsei.ac.kr.

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