and mRNAs are novel RNA targets of the Mei2 RNA-binding protein during early meiosis in .

The RNA-binding protein Mei2 is crucial for meiosis in In mutants, pre-meiotic S-phase is blocked, along with meiosis. Mei2 binds a long non-coding RNA (lncRNA) called meiRNA, which is a 'sponge RNA' for the meiotic inhibitor protein Mmi1. The interaction between Mei2, meiRNA and Mmi1 protein is essential for meiosis. But mutants have stronger and different phenotypes than meiRNA mutants, since arrests before pre-meiotic S, while the meiRNA mutant arrests after pre-meiotic S but before meiosis. This suggests Mei2 may bind additional RNAs. To identify novel RNA targets of Mei2, which might explain how Mei2 regulates pre-meiotic S, we used RNA immunoprecipitation and cross-linking immunoprecipitation. In addition to meiRNA, we found the mRNAs for (which encodes Mmi1) and for the S-phase transcription factor There were also three other RNAs of uncertain relevance. We suggest that at meiotic initiation, Mei2 may sequester mRNA to help allow pre-meiotic S, and then may bind both meiRNA and mRNA to inactivate Mmi1 at two levels, the protein level (as previously known), and also the mRNA level, allowing meiosis. We call Mei2-meiRNA a 'double sponge' (i.e. binding both an mRNA and its encoded protein).