reSeArCH Letter
stresses^26 (Extended Data Fig. 5b). However, translation was detectable
one hour after the cessation of heat shock (Extended Data Fig. 5c, d). At
this time point, transcripts containing four or more m^6 A sites showed
significantly reduced translational efficiency in wild-type relative to
knockout cells (Fig. 4g, Supplementary Table 2). Therefore, polyme-
thylated mRNAs are preferentially repressed, potentially as a result of
their phase separation.
Our studies demonstrate that m^6 A regulates the fate of cytosolic
mRNA by scaffolding DF proteins, which leads to the formation of
phase-separated DF–m^6 A-mRNA complexes that then partition into
phase-separated structures in cells. This effect is especially efficient
for polymethylated mRNAs, which can scaffold multiple DF proteins.
Although mRNAs are targeted to diverse intracellular condensates
through diverse RNA–RNA and RNA–protein interactions^27 , the pres-
ence of m^6 A further enhances the partitioning into these structures.
Furthermore, singly methylated and polymethylated mRNAs have
different fates, which probably reflect their different abilities to pro-
mote LLPS. Notably, monomethylated and polymethylated mRNAs are
linked to distinct cellular functions and biological processes (Extended
Data Fig. 6a, b). LLPS may therefore influence specific cellular pro-
cesses by selectively affecting the translation of mRNAs on the basis of
their polymethylation status.
Unlike other forms of RNA-scaffolded LLPS, m^6 A provides a mecha-
nism for regulated phase separation based on the multivalency of m^6 A.
Because m^6 A levels might vary in different disease, differentiation or
signalling contexts^14 ,^28 , the phase-separated transcriptome will be
encoded, in part, by the cell context-specific distribution and number
of m^6 A sites in each mRNA (Extended Data Fig. 7a, b). The efficiency
of m^6 A-dependent regulation of an mRNA will probably be determined
by pathways that control the efficiency of LLPS of the DF proteins.Online content
Any methods, additional references, Nature Research reporting summaries, source
data, extended data, supplementary information, acknowledgements, peer review
information; details of author contributions and competing interests are available
at https://doi.org/10.1038/s41586-019-1374-1.Received: 17 January 2019; Accepted: 13 June 2019;
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