| LINEs (Long interspersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements) are transposable elements (red) that move via target-primed reverse transcription. An intact LINE element (about 6 kb) is an autonomous element that encodes its own transposition proteins in two open reading frames (ORF1 and ORF2). SINE elements are much shorter (100-300 bp) and are thought to translocate using LINE-encoded proteins. The 3' ends of both elements consist of polyA sequences of variable length and both are flanked by target-site duplications (TSDs), also of variable length (see Figure 13-8.2). Both have internal promoters, which are therefore copied during transcription, ensuring that the translocated copy contains the means of its own duplication. |
