The ORF1 protein encoded by LINE-1: structure and function during L1 retrotransposition - PubMed (original) (raw)

The ORF1 protein encoded by LINE-1: structure and function during L1 retrotransposition

Sandra L Martin. J Biomed Biotechnol. 2006.

Abstract

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.

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Figures

Figure 1

Figure 1

Schematic representation of the ORF1 protein. The thin bar for each species represents the entire length of the protein. Thicker bars represent the coiled-coil (gray, based upon coils analysis [10]) and conserved domains (black, based upon multiple-sequence alignments using T-Coffee [11]). These two domains overlap in the human, rabbit, and fish, but not the two mouse or rat ORF1 protein sequences, as indicated. Sequences used were mouse A101 (Q91V68l, [12]), mouse L1spa (O54849, [13]), rat (Q63303), human L1rp (AAD39214, [14]), rabbit ([15], not in GenBank), and fish swimmer (AAD02927, [16]). The two mouse and the human ORF1 protein sequences are from retrotransposition-competent elements; the other sequences are from untested elements. A model for the trimeric structure of mouse L1 and its role in TPRT appeared in [17] by Martin et al.

References

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