Abstract
N (6)-methyladenosine (m(6)A) is the most prevalent modified nucleotide in mRNA, and it has important functions in mRNA regulation. However, our understanding of the specific functions of m(6)A along with its cytosolic readers, the YTHDF proteins, has changed substantially in recent years. The original view was that different m(6)A sites within an mRNA could have different functions depending on which YTHDF paralog was bound to it, with bound YTHDF1 inducing translation, while bound YTHDF2 induced mRNA degradation. As a result, each YTHDF was proposed to have unique physiologic roles that arise from their unique binding properties and regulatory effects on mRNA. More recent data have called much of this into question, showing that all m(6)A sites bind all YTHDF proteins with equal ability, with a single primary function of all three YTHDF proteins to mediate mRNA degradation. Here, we describe the diverse technical concerns that led to the original model being questioned and the newer data that overturned this model and led to the new understanding of m(6)A and YTHDF function. We also discuss how any remaining questions about the functions of the YTHDF proteins can be readily resolved.