Figure 2.

Recognition of microbial RNA and DNA by cytoplasmic pattern recognition receptors. RIG-I and MDA5 recognize 5'-triphosphate ssRNA and dsRNA from RNA viruses and trigger signaling cascades via a CARD-containing adaptor molecule, IPS-1. IPS-1 induces the expression of genes for type I interferons and pro-inflammatory cytokines by activating transcription factors of the IRF and NFκB families. The role of LGP2 in RNA virus recognition is unclear and LGP2 has been proposed to inhibit RIG-I activity. DAI recognizes dsDNA and induces gene expression through an unknown adaptor molecule. Modular structures of the receptor proteins are shown with the abbreviations of the domains as follows: CARD, caspase activating recruitment domains; helicase, RNA-binding domain; RD, repressor domain; TM, transmembrane domain; Zα and Zβ, Z-DNA binding domain α and β; D3, tentative name for an additional DNA-binding region; SD, signaling domain.