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Molecular and Cellular Biology, January 2001, p. 100-108, Vol. 21, No. 1
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.100-108.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Sequence-Specific Recognition and Cleavage of Telomeric Repeat (TTAGG)n by Endonuclease of Non-Long Terminal Repeat Retrotransposon TRAS1

Tomohiro Anzai, Hidekazu Takahashi, and Haruhiko Fujiwara*

Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

Received 13 March 2000/Returned for modification 4 May 2000/Accepted 13 October 2000

The telomere of the silkworm Bombyx mori consists of (TTAGG/CCTAA)n repeats and harbors a large number of telomeric repeat-specific non-long terminal repeat retrotransposons, such as TRAS1 and SART1. To understand how these retrotransposons recognize and integrate into the telomeric repeat in a sequence-specific manner, we expressed the apurinic-apryrimidinic endonuclease-like endonuclease domain of TRAS1 (TRAS1 EN), which is supposed to digest the target DNA, and characterized its enzymatic properties. Purified TRAS1 EN could generate specific nicks on both strands of the telomeric repeat sequence between T and A of the (TTAGG)n strand (bottom strand) and between C and T of the (CCTAA)n strand (top strand). These sites are consistent with insertion sites expected from the genomic structure of boundary regions of TRAS1. Time course studies of nicking activities on both strands revealed that the cleavages on the bottom strand preceded those on the top strand, supporting the target-primed reverse transcription model. TRAS1 EN could cleave the telomeric repeats specifically even if it was flanked by longer tracts of nontelomeric sequence, indicating that the target site specificity of the TRAS1 element was mainly determined by its EN domain. Based on mutation analyses, TRAS1 EN recognizes less than 10 bp around the initial cleavage site (upstream 7 bp and downstream 3 bp), and the GTTAG sequence especially is essential for the cleavage reaction on the bottom strand (5'. . . TTAGGTT down-arrow  AGG . . . 3'). TRAS1 EN, the first identified endonuclease digesting telomeric repeats, may be used as a genetic tool to shorten the telomere in insects and some other organisms.

* Corresponding author. Mailing address: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan. Phone and Fax: 81-3-5841-4447. E-mail: haruh{at}k.u-tokyo.ac.jp.

Molecular and Cellular Biology, January 2001, p. 100-108, Vol. 21, No. 1
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.100-108.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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