The Functions of N6-Methyladenosine in Nuclear RNAs

N⁶-methyladenosine (m⁶A) is one of the most common modifications in both eukaryotic and prokaryotic mRNAs. It has been experimentally confirmed that m⁶A methylation is involved in the regulation of stability and translation of various mRNAs. Until recently, the majority of m⁶A-related studies have been focused on the cytoplasmic functions of this modification. Here, we review new data on the role of m⁶A 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 m⁶A 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.