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Unformatted text preview: 435 13.3 Transposable elements in eukaryotes Retroviruses encode at least three proteins that take part in viral replication: the products of the gag, pol, and env genes. The gag-encoded protein has a role in the mat- uration of the RNA genome, pol encodes the all- important reverse transcriptase, and env encodes the structural protein that surrounds the virus. This protein is necessary for the virus to leave the cell to infect other cells. Interestingly, Ty1 elements have genes related to gag and pol but not env . These features led to the hypothesis that, like retroviruses, Ty1 elements are transcribed into RNA transcripts that are copied into double-stranded DNA by the reverse transcriptase. However, unlike retro- viruses, Ty1 elements cannot leave the cell, because they do not encode env . Instead, the double-stranded DNA copies are inserted back into the genome of the same cell. These steps are diagrammed in Figure 13-16....
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- Spring '08