Exon shuffling by L1 retrotransposition

Long interspersed nuclear elements (LINE-1s or L1s) are the most abundant r etrotransposons in the human genome, and they serve as major sources of rev erse transcriptase activity. Engineered L1s retrotranspose at high frequenc y in cultured human cells. Here it is shown that L1s insert into transcribe d genes and retrotranspose sequences derived from their 3' flanks to new ge nomic Locations. Thus, retrotransposition-competent L1s provide a vehicle t o mobilize non-L1 sequences, such as exons or promoters, into existing gene s and may represent a general mechanism for the evolution of new genes.