Figure 4.

Domain analysis of the LON protease. Human cells have several LON protease paralogs. The domain organization of one of them, which is localized in mitochondria, is shown on the top panel. It consists of three domains: N-terminal LON domain (LON-N), which possesses ATP-binding and proteolytic activity and present in all LON proteins; the ATPase family associated with various cellular activities (AAA) domain, which has a chaperone-like function; and the C-terminal LON domain (LON-C), which also has a proteolytic activity. The second one, homologous to the LON protease fused to the VHL protein in fugu (bottom), is shown in the middle panel. Flies and worms possess the LON protease, homologous to the one shown on the top panel, but do not possess the single-domain LON ortholog.