Alu elements in human genes. (a) A typical gene, with exons as boxes and introns as lines. Alu elements (arrows) are found at multiple locations, primarily in introns, and in either orientation (black or gray shading). (b) Part of the gene from (a) is shown after transcription; inverted Alu elements can base-pair to give dsRNA structures that serve as substrates for ADAR editing. (c) Editing may lead to one or more consequences (see text for details).