Human L1 Retrotransposition: cisPreference versus trans Complementation

Abstract

Long interspersed nuclear elements (LINEs or L1s) comprise approximately 17% of human DNA; however, only about 60 of the ∼400,000 L1s are mobile. Using a retrotransposition assay in cultured human cells, we demonstrate that L1-encoded proteins predominantly mobilize the RNA that encodes them. At much lower levels, L1-encoded proteins can act in trans to promote retrotransposition of mutant L1s and other cellular mRNAs, creating processed pseudogenes. Mutant L1 RNAs are mobilized at 0.2 to 0.9% of the retrotransposition frequency of wild-type L1s, whereas cellular RNAs are mobilized at much lower frequencies (ca. 0.01 to 0.05% of wild-type levels). Thus, we conclude that L1-encoded proteins demonstrate a profoundcis preference for their encoding RNA. This mechanism could enable L1 to remain retrotransposition competent in the presence of the overwhelming number of nonfunctional L1s present in human DNA.

ACKNOWLEDGMENTS

We thank Anne Marie DesLauriers at the University of Michigan Flow Core for help with flow cytometry, Robert Lyons at the University of Michigan DNA Sequencing Core for help with oligonucleotide synthesis and DNA sequencing, and Ali Lotia for help with generating computer graphics. We thank David Ginsburg for providing pAI1 cDNAs. We thank Alice Telesnitsky, John Goodier, Eline Luning Prak, Tom Glaser, Dennis Hartigan-O'Connor, and current members of the Moran Lab for critical reading of the manuscript and for helpful discussions during the course of this work.

This work was supported in part by a Damon Runyon Scholar Award (J.V.M.) and National Institutes of Health grants GM60518 (J.V.M.) and CA16519 (J.D.B.).