Molecular biology: Bound to splice

A dominant role for meiosis-specific 3' RNA processing in controlling expression of a fission yeast cyclin gene

Meiotic gene regulation provides a rich source of insight into mechanisms of temporal control during development. We previously reported that accumulation of many meiotic mRNAs in fission yeast is governed by changes in 3' RNA processing and elucidated the molecular basis of this regulatory mechanism for an early meiotic gene. Here, we report that cleavage/polyadenylation is also the nexus of negative control for middle meiotic genes. Parallel profiles of splicing and polyadenylation are observed over a meiotic time course for both rem1 and spo4 but not for a constitutive control gene. Nevertheless, polyadenylation of rem1 transcripts is restricted to meiosis by a splicing-independent mechanism. Through systematic sequence substitutions, we identified a negative control region (NCR) located upstream of the rem1 transcription start site and found that it is required to block 3' RNA processing in proliferating cells. Ablation of the NCR relieves inhibition regardless of whether the intron is present, absent, or carries splice site mutations. Consistent with the previous report of a polypeptide encoded by the first exon of rem1, we discovered a second 3' processing site just downstream from the 5' splice site. Polyadenylation within the intron is activated concurrent with the downstream site during meiosis, is controlled by the NCR, and is enhanced when splicing is blocked via 5' junction or branch point mutations. Taken together, these data suggest a novel regulatory mechanism in which a 5' element modulates the dynamic interplay between splicing and polyadenylation.