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Journal of Biomedicine and Biotechnology
Volume 2006, Article ID 45621, 6 pages
Mini-Review Article

The ORF1 Protein Encoded by LINE-1: Structure and Function During L1 Retrotransposition

Department of Cell and Developmental Biology, School of Medicine, University of Colorado, Fitzsimons Campus, PO Box 6511, Mail Stop 8108, Aurora, CO 80045, USA

Received 17 September 2005; Revised 10 December 2005; Accepted 13 December 2005

Copyright © 2006 Sandra L. Martin. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


LINE-1 or L1 is an autonomous non-LTR retrotransposon in mammals. Retrotransposition requires the function of the two L1-encoded polypeptides, ORF1p and ORF2p. Early recognition of regions of homology between the predicted amino acid sequence of ORF2 and known endonuclease and reverse transcriptase enzymes led to testable hypotheses regarding the function of ORF2p in retrotransposition. As predicted, ORF2p has been demonstrated to have both endonuclease and reverse transcriptase activities. In contrast, no homologs of known function have contributed to our understanding of the function of ORF1p during retrotransposition. Nevertheless, significant advances have been made such that we now know that ORF1p is a high-affinity RNA-binding protein that forms a ribonucleoprotein particle together with L1 RNA. Furthermore, ORF1p is a nucleic acid chaperone and this nucleic acid chaperone activity is required for L1 retrotransposition.