Structural insights into the specific recognition of DSR by the YTH domain containing protein Mmi1.

Meiosis is one of the most dramatic differentiation programs accompanied by a striking change in gene expression profiles in fission yeast Schizosaccharomyces pombe. Whereas a number of meiosis-specific transcripts are expressed untimely in mitotic cells, and the entry of meiosis will be blocked as the accumulation of meiosis-specific mRNAs in the mitotic cells. A YTH domain containing protein Mmi1 was identified as a pivotal effector in a post-transcriptional event termed selective elimination of meiosis-specific mRNAs. Mmi1 can recognize and bind a class of meiosis-specific transcripts expressed inappropriately in mitotic cells, which all contain a conservative region called DSR, as a mark to remove them in cooperation with nuclear exosomes. Here we report the 1.6 Å resolution crystal structure of the Mmi1-YTH domain in complex with a high consensus hexanucleotide motif, which is multiple copied in the DSR region. Our structure observations, supported by site-directed mutations of key residues illustrate the mechanism for specific recognition of DSR-RNA by Mmi1. Moreover, different from other YTH domain family proteins, Mmi1-YTH domain has a distinctive RNA-binding properties although it has a similar fold as other ones.