Variable patterns of retrotransposition in different HeLa strains provide mechanistic insights into SINE RNA mobilization processes.

elements are non-autonomous Short INterspersed Elements (SINEs) derived from the gene that are present at over one million copies in human genomic DNA. mobilizes by a mechanism known as retrotransposition, which requires the Long INterspersed Element-1 (LINE-1 or L1) -encoded protein (ORF2p). Here, we demonstrate that HeLa strains differ in their capacity to support retrotransposition. Human elements retrotranspose efficiently in HeLa-HA and HeLa-CCL2 ( -permissive) strains, but not in HeLa-JVM or HeLa-H1 ( -nonpermissive) strains. A similar pattern of retrotransposition was observed for other -derived SINEs and -derived SINEs. In contrast, mammalian LINE-1s, a zebrafish LINE, a human - ( ) element, and an -containing messenger RNA can retrotranspose in all four HeLa strains. Using an reverse transcriptase-based assay, we show that RNAs associate with ORF2p and are converted into cDNAs in both -permissive and -nonpermissive HeLa strains, suggesting that - and -derived SINE RNAs use strategies to 'hijack' L1 ORF2p that are distinct from those used by elements and -containing mRNAs. These data further suggest ORF2p associates with the RNA poly(A) tract in both -permissive and -nonpermissive HeLa strains, but that retrotransposition is blocked after this critical step in -nonpermissive HeLa strains.