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Molecular and Cellular Biology, January 2001, p. 467-475, Vol. 21, No. 2
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.2.467-475.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Nucleic Acid Chaperone Activity of the ORF1 Protein from the Mouse LINE-1 Retrotransposon

Sandra L. Martin1,2,* and Frederic D. Bushman2

Department of Cellular and Structural Biology, University of Colorado School of Medicine, Denver, Colorado 80262,1 and Infectious Disease Laboratory, The Salk Institute, La Jolla, California 920372

Received 26 July 2000/Returned for modification 11 September 2000/Accepted 22 October 2000

Non-LTR retrotransposons such as L1 elements are major components of the mammalian genome, but their mechanism of replication is incompletely understood. Like retroviruses and LTR-containing retrotransposons, non-LTR retrotransposons replicate by reverse transcription of an RNA intermediate. The details of cDNA priming and integration, however, differ between these two classes. In retroviruses, the nucleocapsid (NC) protein has been shown to assist reverse transcription by acting as a "nucleic acid chaperone," promoting the formation of the most stable duplexes between nucleic acid molecules. A protein-coding region with an NC-like sequence is present in most non-LTR retrotransposons, but no such sequence is evident in mammalian L1 elements or other members of its class. Here we investigated the ORF1 protein from mouse L1 and found that it does in fact display nucleic acid chaperone activities in vitro. L1 ORF1p (i) promoted annealing of complementary DNA strands, (ii) facilitated strand exchange to form the most stable hybrids in competitive displacement assays, and (iii) facilitated melting of an imperfect duplex but stabilized perfect duplexes. These findings suggest a role for L1 ORF1p in mediating nucleic acid strand transfer steps during L1 reverse transcription.

* Corresponding author. Mailing address: Department of Cellular and Structural Biology, B111, University of Colorado School of Medicine, 4200 E. Ninth Ave., Denver, CO 80262. Phone: (303) 315-6284. Fax: (303) 315-4729. E-mail: sandy.martin{at}uchsc.edu.

Molecular and Cellular Biology, January 2001, p. 467-475, Vol. 21, No. 2
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.2.467-475.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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