The functions of RNA N6-methyladenosine in the nucleus

N6-methyladenosine (m6A) is one of the most abundant modifications of both eukaryotic and prokaryotic mRNAs. Recent years witnessed an accumulation of a large volume of experimental data on the involvement of m6A methylation in the regulation of stability and translation of different mRNAs. Remarkably, up until recently, the majority of such m6A-related studies have been focused on cytoplasmic functions of this modification. In this review, we overview a number of novel studies revealing the role of m6A in several key biological processes occurring in cellular nucleus, such as transcription, organization of chromatin, splicing, nuclear-cytoplasmic transport, and R-loop metabolism. Based on this analysis, we propose a model where modifications present on nuclear RNAs represent an additional layer of regulation of gene expression, that, together with DNA methylation and histone modifications, determines chromatin structure and function in various biological contexts.