Role of Hakai in m 6 A modification pathway in Drosophila.

N6-methyladenosine (m6A), the most abundant internal modification in eukaryotic mRNA, is installed by a multi-component writer complex; however, the exact roles of each component remain poorly understood. Here we show that a potential E3 ubiquitin ligase Hakai colocalizes and interacts with other m6A writer components, and Hakai mutants exhibit typical m6A pathway defects in Drosophila, such as lowered m6A levels in mRNA, aberrant Sxl alternative splicing, wing and behavior defects. Hakai, Vir, Fl(2)d and Flacc form a stable complex, and disruption of either Hakai, Vir or Fl(2)d led to the degradation of the other three components. Furthermore, MeRIP-seq indicates that the effective m6A modification is mostly distributed in 5’ UTRs in Drosophila, in contrast to the mammalian system. Interestingly, we demonstrate that m6A modification is deposited onto the Sxl mRNA in a sex-specific fashion, which depends on the m6A writer. Together, our work not only advances the understanding of mechanism and regulation of the m6A writer complex, but also provides insights into how Sxl cooperate with the m6A pathway to control its own splicing. Drosophila m6A writer complex regulates alternative splicing of the Sex-lethal gene. Here the authors show that a potential E3 ligase Hakai interacts with the fly m6A writer complex and that m6A level is reduced in Hakai mutant flies.