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. Author manuscript; available in PMC: 2013 Sep 26.
Published in final edited form as: Mol Cells. 2012 Nov 6;34(6):509–516. doi: 10.1007/s10059-012-0242-8

Figure 1. Schematics of the major classes of retrotransposons.

Figure 1

Typical sequence length of each retrotransposon is according to the Repbase database (http://www.girinst.org/repbase/). Alu contains two RNA polymerase III promoters, but does not encode proteins. L1 has a polymerase II promoter in the 5′ UTR region and two ORFs. SVA consists of hexamer repeat regions, Alu-like regions, variable number of tandem repeats (VNTR), SINE-R, and polyA regions, but does not encode proteins. Because there is no internal promoter, SVA may be transcribed using 5′-flanking promoters. LTR retrotransposon contains a promoter in the LTR, and the transcript produces group specific antigen (gag), protease (pro), reverse transcriptase (pol), and envelope (env) proteins.