Archaea employ small RNAs as regulators

In addition to well-characterized non-coding RNAs like ribosomal RNAs and transfer RNAs, a plethora of non-coding RNAs exists in organisms of all three domains of life (Hüttenhofer et al., 2005; Storz, 2002). In Eukaryotes the non-coding miRNAs and siRNAs are small RNAs of about 21 nucleotides and they function primarily by base pairing with their target mRNAs, mediating the inhibition of translation or triggering degradation as part of the RISC complex (Krol et al., 2010). The miRNAs act always as part of the RISC complex, where they primarily bind to the Argonaute protein. Homologs to Argonaute proteins have been detected in Archaea but the function of the archaeal Argonaute proteins is not clear yet (Li et al., 2010; Makarova et al., 2009).