Time frame of events influencing Alu element activity. (1) De novo Alu insertion acquiring new 5′ transcription regulators and 3′ unique sequence which dramatically affect future retrotransposition efficiency. In addition, epigenetic changes will impact transcriptional capability of the Alu insert. (2) Alu A-tail length shortening occurs rapidly after insertion to squelch future activity. (3) The quick introduction of heterogeneity in the A-tail through microsatellite expansion causing an additional reduction in retrotransposition efficiency. (4) Slower and random accumulation of random mutations throughout the element including mutations to the A and B box reducing Alu transcription efficiency, mutations in the A-tail increasing heterogeneity, and mutations throughout the left and right monomers reducing overall identity with a consensus sequence possibly affecting RNA stability and structure.
