In mammals, the most abundant internal RNA modification is covalent linkage of a methyl group to the RNA adenine N6 position (N6-methyladenosine or m6A). Functionality of this modification is evidenced by findings that mice engineered to lack m6A de-methylases display abnormalities in energy expenditure and fertility. We reported that m6A methyltransferases are required to maintain mouse embryonic stem cells at their ground state. However, how m6A RNA methylation exerts these functions remains unclear. Recent evidence from our work and others suggests that a major functional mechanism of m6A RNA methylation is to destabilize RNA. In this proposal, we will test this hypothesis by characterizing newly discovered mammalian m6A methyltransferases (Aim 1), identifying the RNA sequence or structure that imparts methylation specificity (Aim 2), and determining whether m6A methylation regulates RNA stability by interacting with the human antigen R - microRNA regulatory pathway (Aim 3). We believe that these are pioneering studies in identifying molecular mechanisms underlying m6A RNA methylation in mammalian cells at the molecular and cellular levels. Fundamental RNA regulatory mechanisms revealed may create a new paradigm for eukaryotic gene regulation and stimulate studies of other modifications of coding or noncoding RNAs. Furthermore, our results could provide strategies to manipulate stability of specific RNAs to maintain pluripotent stem cells in culture as an unlimited source of material for cell therapy.