We examined three RNA-protein complexes: 1) argonaute 2 with bound guide RNA and a target RNA , 2) CasPhi-2 bound to CRISPR RNA and 3) Retinoic acid-inducible gene I C268F in complex with double-stranded RNA (Figure ). For simplicity, we will refer to these complexes with the abbreviations Ago2, Cas12j and RIG-I, respectively. Ago2 forms the base of the RNA-induced silencing complex (RISC) which inhibits gene expression by binding to the mRNA guided by the short siRNA . Cas12j is an RNA-guided nuclease that initiates CRISPR RNA complementary double-stranded DNA unwinding and cleavage in bacteriophages . RIG-I is a cytosolic receptor that recognizes viral double-stranded RNA molecules as an immune sensor . These complexes were chosen because they included only protein and RNA chains, were cytosolic, relatively small (contained less than 8000 of modeled non-hydrogen atoms), had not too many missing residues in their structures and all of them had a large interaction surface between the RNA(s) and the protein.