Figure 2. Proposed model for the turnover of mature miRNAs based on combined evidence from plants, algae and metazoans.

Figure 2

Proposed model for the turnover of mature miRNAs based on combined evidence from plants, algae and metazoans. A miRNA/miRNA* duplex is loaded into AGO and the two strands are separated by a poorly characterized mechanism. The unwound miRNA* strand is rapidly eliminated by an unknown enzyme(s). In C. reinhardtii, MUT68 (a terminal nucleotidyltransferase) and RRP6 (a 3′-to-5′ exoribonuclease) may be part of a quality control mechanism to eliminate dysfunctional or damaged miRNAs that are loaded into Argonautes, in kinetic competition with the methyltransferase HEN1 (see text for details). Both C. elegans XRN-2 (a 5′-to-3′ exoribonuclease) and A. thaliana SDN enzymes (3′-to-5′ exoribonucleases) may contribute to the decay of mature small RNAs dissociated from Argonautes (see text for details). For simplicity, the AGO-bound miRNA strand is shown methylated, as it occurs in plants and some algae, but C. elegans miRNAs would not undergo this modification.

From: Turnover of Mature miRNAs and siRNAs in Plants and Algae

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