The Functions of N6-Methyladenosine in Nuclear RNAs

N-6-methyladenosine (m(6)A) is one of the most common modifications in both eukaryotic and prokaryotic mRNAs. It has been experimentally confirmed that m(6)A methylation is involved in the regulation of stability and translation of various mRNAs. Until recently, the majority of m(6)A-related studies have been focused on the cytoplasmic functions of this modification. Here, we review new data on the role of m(6)A in several key biological processes taking place in the cell nucleus, such as transcription, chromatin organization, splicing, nuclear-cytoplasmic transport, and R-loop metabolism. Based on analysis of these data, we suggest that m(6)A methylation of nuclear RNAs is another level of gene expression regulation which, together with DNA methylation and histone modifications, controls chromatin structure and functioning in various biological contexts.