Ssu72 is a phosphatase essential for transcription termination of snoRNAs and specific mRNAs in yeast

Abstract

C.Ganem and F.Devaux contributed equally to this workSsu72 is an essential yeast protein that is involved in transcription. It physically interacts with transcription initiation and termination complexes. In this report, we provide evidence that Ssu72 is a phosphatase that physically interacts with the CTD kinase Kin28 and functionally interacts with the CTD phosphatase Fcp1. A genome-wide expression analysis of mutant ssu72-ts69 during growth in complete medium revealed a number of defects, including the accumulation of a limited number of mRNAs and the readthrough transcription of small nucleolar RNAs and of some mRNAs. We hypothesize that Ssu72 plays a key role in the transcription termination of certain transcripts, possibly by promoting RNA polymerase pausing and release. The possibility that the CTD of the largest subunit of RNA polymerase II is a substrate of Ssu72 is discussed.

Arabidopsis C-terminal domain phosphatase-like 1 and 2 are essential Ser-5-specific C-terminal domain phosphatases

“…The latter model is appealing in light of the finding that a recessive mutation in the plant ABH1 gene encoding a nuclear cap binding protein causes attenuation of ABA induction of at least 18 Arabidopsis genes (4). In contrast, the predominant molecular phenotype of ssu72 mutation is the incomplete termination of small nucleolar RNA and some mRNA transcription by Pol II (40).…”

Yeast Swd2 Is Essential Because of Antagonism between Set1 Histone Methyltransferase Complex and APT (Associated with Pta1) Termination Factor

“…To test whether the 6AU sensitivity of set1⌬ strains could be related to excessive CTD phosphorylation, the two known CTD serine 5 phosphatases Rtr1 (47) and Ssu72 (48,49) were overexpressed from galactose-inducible promoters. Overexpression of Rtr1, but not Ssu72, was able to reverse the 6AU sensitivity of set1⌬ (Fig.…”

“…5). In this model, Swd2 and other APT subunits would contribute to Nrd1-Nab3-Sen1 recruitment either directly or indirectly, an idea supported by the fact that APT mutants show defects in snoRNA termination (27)(28)(29)(30)48).…”

Transcription termination by nuclear RNA polymerases

“…Additionally, mutations in a subcomplex of the cleavage/ polyadenylation machinery, the APT complex (associated with Pta1 [homolog of symplekin]), lead to read-through transcription of certain sn/snoRNA genes (Dheur et al 2003;Ganem et al 2003;Nedea et al 2003;Steinmetz and Brow 2003;Kim et al 2006;Ghazy et al 2009). The APT factors implicated in sn/snoRNA termination include Pti1, a second yeast homolog of CstF-64 that also binds Rna14; Ref2, which interacts with the snoRNPspecific protein Nop1 (Morlando et al 2004); the CTD phosphatase Ssu72 (Ganem et al 2003;Steinmetz and Brow 2003;Kim et al 2006); and Swd2, which is also a component of the Set1 complex (Cheng et al 2004;Dichtl et al 2004). Overexpression of Pti1 inhibits polyadenylation without affecting cleavage, suggesting that Pti1 may function in uncoupling cleavage and polyadenylation during snoRNA 39-end formation (Dheur et al 2003).…”