PROJECT SUMMARY: N6-methyladenosine (m6A), the most abundant nucleotide modification in the transcriptome, has the well- established function of causing instability of modified mRNAs. Importantly, differentiation of hematopoietic stem cells is one of the most-well studied scenarios in which m6A-modified mRNAs appears to be preferentially degraded. Although this degradation process appears to be a highly regulated event to ensure cellular commitment, a clear mechanism of how this event is regulated is missing. My recent work demonstrated that the major mediators of m6A-mRNA degradation are the YTHDF (DF) proteins. Thus, a major goal is to understand how these proteins are regulated to trigger m6A mRNA degradation. My working hypothesis, which is supported by preliminary data, is the existence of a specific DF phosphorylation-code regulating the DF ability to degrade m6A-mRNA. In this proposal, I will map this DF phospho-code, identify the DF targeting kinases, and determine how DF phosphorylation affects the differentiation of hematopoietic stem cells. Overall this proposal may reveal how DF phosphorylation controls m6A mRNA stability and its fundamental role during the differentiation commitment of the hematopoietic stem cells.