N6-methyladenosine residues in an intron-specific region of prolactin pre-mRNA.

Abstract

N6-methyladenosine (m6A) residues occur at internal positions in most cellular and viral RNAs; both heterogeneous nuclear RNA and mRNA are involved. This modffication arises by enzymatic transfer of a methyl group from S-adenosylmethionine to the central adenosine residue in the canonical sequence G/AAC. Thus suggested following the precise localization of m6A in Rous sarcoma virus (18). In that molecule, the modified residues were found bracketing the src splice acceptor site and therefore may influence in some way the accuracy and/or efficiency of processing. Methylation of internal adenosine residues of eucaryotic cell RNA also takes place in the nucleus, as evidenced by the demonstration of m6A in eucaryotic cell heterogeneous nuclear RNA (24). However, previous analysis indicated a conservation of m6A residues during processing and transport to the cytoplasm, suggesting that this modification occurs mainly within exon regions (19). It was therefore of great interest to determine whether m6A occurs in intron-specific regions of eucaryotic precursor RNA. This analysis would identify the temporal relationship between transcription, methylation, and nuclear processing and may assist in developing a concept for the role of this posttranscriptional modification in eucaryotic RNA biogenesis.Attempts have been made to determine the influence of m6A on processing of gene transcripts. Earlier studies with cycloleucine, an inhibitor of S-adenosylmethionine synthetase, suggested that m6A affects the splicing of avian sarcoma virus genomic RNA (34) and processing of CHO cell mRNA (2). This hypothesis is supported by the similarity between the m6A consensus sequences in both eucaryotic and viral RNA and the weakly conserved branch point sequence YNCU(G/A)AC used in intron removal (18,27,40). Camper et al. (5) used the mRNA methylation inhibitor S-tubercidinyl homocysteine to measure the effects of undermethylation on the half-life and cytoplasmic appearance of poly(A)+ RNA in HeLa cells. A significant effect on processing and/or transport of undermethylated mRNA occurred with a delay in its appearance in the cytoplasm, whereas no significant alteration in the cytoplasmic half-life of undermethylated mRNA was observed.

N6‐methyladenosine modification in mRNA: machinery, function and implications for health and diseases

“…Moreover, m 6 A sites in many mRNAs were found to be concentrated within introns [97,98]. Emerging evidence from recent studies strongly supports the functional involvement of m 6 A methylation in splicing.…”

MTA Is an Arabidopsis Messenger RNA Adenosine Methylase and Interacts with a Homolog of a Sex-Specific Splicing Factor

“…Thus, the presence of m 6 A has the potential to affect mRNA secondary structure as well as mRNA-protein and mRNA-snRNA interactions. Little is known of the distribution of m 6 A in nascent mRNA transcripts, but one case of its presence within an intron has been reported (Carroll et al, 1990).…”

NSun2 Promotes Cell Growth via Elevating Cyclin-Dependent Kinase 1 Translation

“…Methylation of the 3=UTR of mRNAs has been described since the late 1980s (36)(37)(38). Recently, studies have revealed that methylation of mRNA other than the 5=-cap structure is a common posttranscriptional modification (39).…”