The yeast RNA methylation complex consists of conserved yet reconfigured components with m6A-dependent and independent roles.

N6-methyladenosine (m6A), the most abundant mRNA modification, is deposited in mammals/insects/plants by m6A methyltransferase complexes (MTC) comprising a catalytic subunit and at least five additional proteins. The yeast MTC is critical for meiosis and was known to comprise three proteins, of which two were conserved. We uncover three novel MTC components (Kar4/Ygl036w-Vir1/Dyn2). All MTC subunits, except for Dyn2, are essential for m6A deposition and have corresponding mammalian MTC orthologues. Unlike the mammalian bipartite MTC, the yeast MTC is unipartite, yet multifunctional. The mRNA interacting module, comprising Ime4, Mum2, Vir1, and Kar4, exerts the MTC's m6A-independent function, while Slz1 enables the MTC catalytic function in m6A deposition. Both functions are critical for meiotic progression. Kar4 also has a mechanistically separate role from the MTC during mating. The yeast MTC constituents play distinguishable m6A-dependent, MTC-dependent, and MTC-independent functions, highlighting their complexity and paving the path towards dissecting multi-layered MTC functions in mammals.

Nora Virus VP4b and ORF1 Circulate in Hemolymph of Infected D. melanogaster with Coordinate Expression of Vago and Vir-1.

Study of the novel RNA virus, Nora virus, which is a persistent, picorna-like virus that replicates in the gut of Drosophila melanogaster offers insight into human innate immunity and other picorna-like viruses. Nora virus infection leads to a locomotor abnormality and upregulation of two candidate target proteins, Vago and Virus-induced RNA 1 (Vir-1). These proteins are uncharacterized in response to Nora virus. We hypothesize that Nora virus is circulating in the hemolymph of Nora virus-infected D. melanogaster, allowing for migration beyond the primary site of replication in the gut. Analysis by qRT-PCR demonstrated biphasic viral load and corresponding vago and vir-1 transcription levels, suggesting transcription of vago and vir-1 occurs in response to viral infection. However, Vir-1 is also present in virus-free D. melanogaster suggesting basal expression or alternative functions. Presence of Nora virus RNA and the Viral Protein 4b (VP4b), in hemolymph of infected D. melanogaster supports the hypothesized circulation of Nora virus in the hemolymph. The study suggests that impaired locomotor function may be due to transport of Nora virus from the gut to the brain via the hemolymph.