Inactivation of fission yeast Erh1 de-represses expression: evidence that Erh1 is a negative regulator of lncRNA termination.

Fission yeast Erh1 exists in a complex with RNA-binding protein Mmi1. Deletion of up-regulates the phosphate homeostasis gene , which is normally repressed by transcription in of a 5' flanking lncRNA. Here we present evidence that de-repression of by eΔ is achieved through precocious 3'-processing/termination of lncRNA synthesis, to wit: (i) Δ does not affect the activity of the or promoters per se; (ii) de-repression by Δ depends on CPF (cleavage and polyadenylation factor) subunits Ctf1, Dis2, Ssu72, Swd22, and Ppn1 and on termination factor Rhn1; (iii) de-repression requires synthesis by the Asp1 IPP kinase of inositol 1-pyrophosphates (1-IPPs); (iv) de-repression is effaced by mutating Thr4 of the RNA polymerase II CTD to alanine; and (v) Δ exerts an additive effect on de-repression in combination with mutating CTD Ser7 to alanine and with deletion of the IPP pyrophosphatase Aps1. These findings point to Erh1 as an antagonist of lncRNA termination in the axis. In contrast, in Δ cells there is a reduction in mRNA and increase in the formation of a read-through transcript, consistent with Mmi1 being an agonist of termination. We envision that Erh1 acts as a brake on Mmi1's ability to promote CPF-dependent termination during lncRNA synthesis. Consistent with this idea, Δ de-repression of was eliminated by mutating the Mmi1-binding sites in the lncRNA.