The first group possesses an N-terminal domain with sequence similarity to the intracellular signaling domains of the Drosophila Toll and mammalian interleukin(IL-) 1 receptors and is referred to as TIR-NB-LRRs or
TNLs. The second group is collectively known as CC-NB-LRRs or CNLs, based on the presence of a predicted N-terminal coiled-coil domain in some, but not all, members of this class.