FIGURE 1. Pseudogene-mediated production of endogenous small interfering RNAs (endo-siRNAs).

Pseudogenes can arise through the copying of a parent gene (by duplication or by retrotransposition). a, An antisense transcript of the pseudogene and an mRNA transcript of its parent gene can then form a double-stranded RNA. b, Pseudogenic endo-siRNAs can also arise through copying of the parent gene as in a and then nearby duplication and inversion of this copy. The subsequent transcription of both copies results in a long RNA, which folds into a hairpin, as one half of it is complementary to its other half. In both a and b, the double-stranded RNA is cut by Dicer into 21-nucleotide endo-siRNAs, which are guided by the RISC complex to interact with, and degrade, the parent gene's remaining mRNA transcripts. The mRNA from genes is in red and that from pseudogenes is in blue. Green arrows indicate DNA rearrangements.