Figure 6.

Alu retroposition model. Poly(A) binding protein (PABP) interacts with the A-tails of the Alu and L1 RNA. The SRP9/14 proteins bind the 5′ end of the Alu RNA, which may help target the RNA to the ribosome and translational machinery. The cap complex of L1 RNA interacts with the PABP in the A-tail, circularizing the RNA. In contrast, Alu RNA, being a pol III, has no cap and thus is not circularized, allowing the A-tail/PABP end free to interact with the L1 cap complex. Because the Alu RNA is in close proximity to the L1 RNA when translation of the retroposition factors occurs, it allows the Alu to compete for the required components for its own retroposition. Details of the model are presented in the Discussion.