Figure 5

Alu elements and post-transcriptional processing of transcripts. (a) The majority of primary transcripts from genes contain Alu elements, both sense and antisense, within their introns. These Alu elements gradually accumulate mutations that can activate cryptic splice sites, or polyadenylation sites, within the Alu. This can lead to alternative splicing of RNAs that can either include a portion of an Alu in the coding region or result in premature termination of translation. Similarly, Alu elements may cause premature termination and polyadenylation resulting in truncated genes. (b) Alu elements in introns located in opposite orientations can fold into secondary structures that are then a major substrate for ADAR (adenosine deaminase that acts on RNA) activity. The edited RNAs may then have cryptic splice sites activated or may also result in retention of the RNA in the nucleus.