Limited effects of m(6)A modification on mRNA partitioning into stress granules

The presence of the m(6)A modification in mammalian mRNAs is proposed to promote mRNA recruitment to stress granules through the interaction with YTHDF proteins. We test this possibility by examining the accumulation of mRNAs in stress granules in both WT and ∆METTL3 mES cells, which are deficient in m(6)A modification. A critical observation is that all m(6)A modified mRNAs partition similarly into stress granules in both wild-type and m(6)A-deficient cells by single-molecule FISH. Moreover, multiple linear regression analysis indicates m(6)A modification explains only 6% of the variance in stress granule localization when controlled for length. Finally, the artificial tethering of 25 YTHDF proteins on reporter mRNAs leads to only a modest increase in mRNA partitioning to stress granules. Since most mammalian mRNAs have 4 or fewer m(6)A sites, and those sites are not fully modified, this argues m(6)A modifications are unlikely to play a significant role in recruiting mRNAs to stress granules. Taken together, these observations argue that m(6)A modifications play a minimal, if any, role in mRNA partitioning into stress granules.