Overview of a phylogenetic tree of 277 NLR proteins. Each sequence is assigned a background color to illustrate species relationships: pink = human, yellow = mouse, blue = zebrafish, green = Takifugu, and turquoise = Tetraodon. The 'canonical' proteins Nod1, Nod2, Nod3, Nod9, CIITA, and Apaf, which show clear homologous relationships between the five species, cluster at the top (rainbow colors). The mammalian Nalp proteins cluster together (pink/yellow region). Each fish has a large group of species-specific proteins (blue, green, and turquoise regions). In addition, Takifugu and Tetraodon share several apparently orthologous gene pairs (green and turquoise region). Apaf, apoptotic protease activating factor; CIITA, major histocompatibility complex class II, transactivator; Nalp, NACHT, leucine rich repeat and PYD containing protein; NLR, nucleotide-binding domain/NACHT domain and leucine rich repeat containing family; Nod, nucleotide oligomerization domain containing protein.