FIGURE 1.

Evolution of anti-NOS2A locus. (A) The chain of evolutionary events suggested by our studies and leading to the creation of the anti-NOS2A locus in the human genome involved partial duplication (indicated by the linked arrows) of an ancestral NOS2A gene coupled to an internal DNA inversion (hatched box) within the duplicated copy (light gray box). Because of such dramatic disruption of the organization, the anti-NOS2A locus cannot produce mature NOS2A mRNA. Instead, it can be transcribed into a NOS2A-related transNAT. (B) Organization of orthologous anti-NOS2A loci in the human (Homo sapiens), orangutan (Pongo pygmaeus), chimpanzee (Pan troglodytes), and rhesus macaque (Macaca mulatta) genomes. Internal DNA inversions are shown by hatched boxes.