An Antisense RNA-mediated Mechanism Eliminates a Meiosis-specific Copper-regulated Transcript in Mitotic Cells
Journal of Biological Chemistry, 2015, 290(37): 22622-22637.
Sense and antisense transcripts produced from convergent gene pairs could interfere with the expression of either partner gene. In Schizosaccharomyces pombe, we found that the iss1( ) gene produces two transcript isoforms, including a long antisense mRNA that is complementary to the meiotic cum1( ) sense transcript, inhibiting cum1( ) expression in vegetative cells. Inhibition of cum1( ) transcription was not at the level of its initiation because fusion of the cum1( ) promoter to the lacZ gene showed that activation of the reporter gene occurs in response to low copper conditions. Further analysis showed that the transcription factor Cuf1 and conserved copper-signaling elements (CuSEs) are required for induction of cum1( )-lacZ transcription under copper deficiency. Insertion of a multipartite polyadenylation signal immediately downstream of iss1( ) led to the exclusive production of a shorter iss1( ) mRNA isoform, thereby allowing accumulation of cum1( ) sense mRNA in copper-limited vegetative cells. This finding suggested that the long iss1( ) antisense mRNA could pair with cum1( ) sense mRNA, thereby producing double-stranded RNA molecules that could induce RNAi. We consistently found that mutant strains for RNAi (dcr1 Delta, ago1 Delta, rdp1 Delta, and clr4 Delta) are defective in selectively eliminating cum1( ) sense transcript in the G(1) phase of the cell cycle. Taken together, these results describe the first example of a copper-regulated meiotic gene repressed by an antisense transcription mechanism in vegetative cells.