ECT2 peptide sequences outside the YTH domain regulate its m6A-RNA binding.

The m⁶A epitranscriptomic mark is the most abundant and widespread internal RNA chemical modification, which through the control of RNA acts as an important factor of eukaryote reproduction, growth, morphogenesis and stress response. The main m⁶A readers constitute a super family of proteins with hundreds of members that share a so-called YTH RNA binding domain. The majority of YTH proteins carry no obvious additional domain except for an Intrinsically Disordered Region (IDR). In Arabidopsis thaliana IDRs are important for the functional specialization among the different YTH proteins, known as Evolutionarily Conserved C-Terminal region, ECT 1 to 12. Here by studying the ECT2 protein and using an in vitro biochemical characterization, we show that full-length ECT2 and its YTH domain alone have a distinct ability to bind m⁶A, conversely to previously characterized YTH readers. We identify peptide regions outside of ECT2 YTH domain, in the N-terminal IDR, that regulate its binding to m⁶A-methylated RNA. Furthermore, we show that the selectivity of ECT2 binding for m⁶A is enhanced by a high uridine content within its neighbouring sequence, where ECT2 N-terminal IDR is believed to contact the target RNA in vivo. Finally, we also identify small structural elements, located next to ECT2 YTH domain and conserved in a large set of YTH proteins, that enhance its binding to m⁶A-methylated RNA. We propose from these findings that some of these regulatory regions are not limited to ECT2 or YTH readers of flowering plants but may be widespread among eukaryotic YTH readers.