Cytosolic signaling adaptor proteins that were initially discovered by their role in the innate immunity (immunity, innate) response of organisms that lack an adaptive immune system. This class of proteins contains three domains, a C-terminal ligand recognition domain, an N-terminal effector-binding domain, and a centrally located nuclear-binding oligomerization domain. Many members of this class contain a C-terminal leucine rich domain which binds to peptidoglycan on the surface of bacteria and plays a role in pathogen resistance.