Functional interplay between Aurora B kinase and Ssu72 phosphatase regulates sister chromatid cohesion

SSUP-72/PINN-1 coordinates RNA-polymerase II 3' pausing and developmental gene expression in C. elegans

During exit from Caenorhabditis elegans (C. elegans) L1 developmental arrest, a network of growth- and developmental genes is activated, many of which are organized into operons where transcriptional termination is uncoupled from mRNA 3'-end processing. CDK-12-mediated Pol II CTD S2 phosphorylation enhances SL2 trans-splicing at downstream operonic genes, preventing premature termination and ensuring proper gene expression for developmental progression. Using a genetic screen, we identified the SSUP-72/PINN-1 module as a suppressor of defects induced by CDK-12 inhibition. Loss of SSUP-72/PINN-1 bypasses the requirement for CDK-12 in post-embryonic development. Genome-wide analyses reveal that SSUP-72, a CTD S5P phosphatase, affects Pol II 3' pausing and regulates intra-operon termination. Our findings establish SSUP-72/PINN-1 as a key regulator of Pol II dynamics, coordinating operonic gene expression and growth during C. elegans post-embryonic development.

Phosphatase Ssu72 Is Essential for Homeostatic Balance Between CD4+ T Cell Lineages

Ssu72, a dual-specificity protein phosphatase, not only participates in transcription biogenesis, but also affects pathophysiological functions in a tissue-specific manner. Recently, it has been shown that Ssu72 is required for T cell differentiation and function by controlling multiple immune receptor-mediated signals, including TCR and several cytokine receptor signaling pathways. Ssu72 deficiency in T cells is associated with impaired fine-tuning of receptor-mediated signaling and a defect in CD4+ T cell homeostasis, resulting in immune-mediated diseases. However, the mechanism by which Ssu72 in T cells integrates the pathophysiology of multiple immune-mediated diseases is still poorly elucidated. In this review, we will focus on the immunoregulatory mechanism of Ssu72 phosphatase in CD4+ T cell differentiation, activation, and phenotypic function. We will also discuss the current understanding of the correlation between Ssu72 in T cells and pathological functions which suggests that Ssu72 might be a therapeutic target in autoimmune disorders and other diseases.

Somatic mosaicism in STAG2-associated cohesinopathies: Expansion of the genotypic and phenotypic spectrum

STAG2 is a component of the large, evolutionarily highly conserved cohesin complex, which has been linked to various cellular processes like genome organization, DNA replication, gene expression, heterochromatin formation, sister chromatid cohesion, and DNA repair. A wide spectrum of germline variants in genes encoding subunits or regulators of the cohesin complex have previously been identified to cause distinct but phenotypically overlapping multisystem developmental disorders belonging to the group of cohesinopathies. Pathogenic variants in STAG2 have rarely been implicated in an X-linked cohesinopathy associated with undergrowth, developmental delay, and dysmorphic features. Here, we describe for the first time a mosaic STAG2 variant in an individual with developmental delay, microcephaly, and hemihypotrophy of the right side. We characterized the grade of mosaicism by deep sequencing analysis on DNA extracted from EDTA blood, urine and buccal swabs. Furthermore, we report an additional female with a novel de novo splice variant in STAG2. Interestingly, both individuals show supernumerary nipples, a feature that has not been reported associated to STAG2 before. Remarkably, additional analysis of STAG2 transcripts in both individuals showed only wildtype transcripts, even after blockage of nonsense-mediated decay using puromycin in blood lymphocytes. As the phenotype of STAG2-associated cohesinopathies is dominated by global developmental delay, severe microcephaly, and brain abnormalities, we investigated the expression of STAG2 and other related components of the cohesin complex during Bioengineered Neuronal Organoids (BENOs) generation by RNA sequencing. Interestingly, we observed a prominent expression of STAG2, especially between culture days 0 and 15, indicating an essential function of STAG2 in early brain development. In summary, we expand the genotypic and phenotypic spectrum of STAG2-associated cohesinopathies and show that BENOs represent a promising model to gain further insights into the critical role of STAG2 in the complex process of nervous system development.

Ssu72-HNF4α signaling axis classify the transition from steatohepatitis to hepatocellular carcinoma

Growing evidence suggests a mechanistic link between steatohepatitis and hepatocellular carcinoma (HCC). However, the lack of representative animal models hampers efforts to understand pathophysiological mechanisms underlying steatohepatitis-related HCC. We found that liver-specific deletion of Ssu72 phosphatase in mice, leads to a high incidence of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, but not HCC. However, loss of Ssu72 drastically increased the probability of HCC developing, as well as the population of hepatic progenitors, in various chemical and metabolic syndrome-induced HCC models. Importantly, hepatic Ssu72 loss resulted in the induction of mature hepatocyte-to-progenitor cell conversion, by dedifferentiation orchestrated by Ssu72-mediated hypo-phosphorylation of hepatocyte nuclear factor 4α (HNF4α), a master regulator of hepatocyte function. Our findings suggest that Ssu72-mediated HNF4α transcription contributes to the progression of steatohepatitis-associated HCC by regulating the dedifferentiation potential of hepatocytes. Thus, targeting the Ssu72-mediated HNF4α signaling that underlies the pathogenesis of steatohepatitis-associated HCC development could be a novel therapeutic intervention for steatohepatitis-associated HCC.

Mammalian Ssu72 phosphatase preferentially considers tissue-specific actively transcribed gene expression by regulating RNA Pol II transcription

Reversible phosphorylation of the C-terminal domain (CTD) of RNA polymerase II (Pol II) is essential for gene expression control. How altering the phosphorylation of the CTD contributes to gene expression in mammalian systems remains poorly understood.

Methods: Primary mouse embryonic fibroblasts, hepatocytes, and embryonic stem cells were isolated from conditional Ssu72^f/f mice. To knockout the mouse Ssu72 gene, we infected the cells with adenoviruses of incorporated luciferase and Cre recombinase, respectively. RNA sequencing, ChIP sequencing, ChIP assay, immunoblot analyses, qRT-PCR assay, and immunostaining were performed to gain insights into the functional mechanisms of Ssu72 loss in Pol II dynamics.

Results: Using primary cells isolated from Ssu72 conditional knockout and transgenic mice, we found that mammalian Ssu72-mediated transcriptional elongation rather than polyadenylation or RNA processing contributed to the transcriptional regulation of various genes. Depletion of Ssu72 resulted in aberrant Pol II pausing and elongation defects. Reduced transcriptional elongation efficiency tended to preferentially affect expression levels of actively transcribed genes in a tissue-specific manner. Furthermore, Ssu72 CTD phosphatase seemed to regulate the phosphorylation levels of CTD Ser2 and Thr4 through accurate modulation of P-TEFb activity and recruitment.

Conclusions: Our findings demonstrate that mammalian Ssu72 contributes to the transcription of tissue-specific actively transcribed gene expression by regulating reciprocal phosphorylation of Pol II CTD.

Ssu72 phosphatase directly binds to ZAP-70, thereby providing fine-tuning of TCR signaling and preventing spontaneous inflammation

ZAP-70 is required for the initiation of T cell receptor (TCR) signaling, and Ssu72 is a phosphatase that regulates RNA polymerase II activity in the nucleus. However, the mechanism by which ZAP-70 regulates the fine-tuning of TCR signaling remains elusive. Here, we found that Ssu72 contributed to the fine-tuning of TCR signaling by acting as tyrosine phosphatase for ZAP-70. Affinity purification-mass spectrometry and an in vitro assay demonstrated specific interaction between Ssu72 and ZAP-70 in T cells. Upon TCR stimulation, Ssu72-deficient T cells increased the phosphorylation of ZAP-70 and downstream molecules and exhibited hyperresponsiveness, which was restored by reducing ZAP-70 phosphorylation. In vitro assay demonstrated that recombinant Ssu72 reduced tyrosine phosphorylation of ZAP-70 via phosphatase activity. Cd4-CreSsu72 ^fl/fl mice showed a defect in the thymic development of invariant natural killer T cells and reductions in CD4⁺ and CD8⁺ T cell numbers in the periphery but more CD44^hiCD62L^lo memory T cells and fewer CD44^loCD62L^hi naïve T cells, compared with wild-type mice. Furthermore, Cd4-CreSsu72 ^fl/fl mice developed spontaneous inflammation at 6 mo. In conclusion, Ssu72 phosphatase regulates the fine-tuning of TCR signaling by binding to ZAP-70 and regulating its tyrosine phosphorylation, thereby preventing spontaneous inflammation.

Ssu72 is a T-cell receptor-responsive modifier that is indispensable for regulatory T cells

The homeostatic balance between effector T cells and regulatory T cells (Tregs) is crucial for adaptive immunity; however, epigenetic programs that inhibit phosphorylation to regulate Treg development, peripheral expression, and suppressive activity are elusive. Here, we found that the Ssu72 phosphatase is activated by various T-cell receptor signaling pathways, including the T-cell receptor and IL-2R pathways, and localizes at the cell membrane. Deletion of Ssu72 in T cells disrupts CD4+ T-cell differentiation into Tregs in the periphery via the production of high levels of the effector cytokines IL-2 and IFNγ, which induce CD4+ T-cell activation and differentiation into effector cell lineages. We also found a close correlation between downregulation of Ssu72 and severe defects in mucosal tolerance in patients. Interestingly, Ssu72 forms a complex with PLCγ1, which is an essential effector molecule for T-cell receptor signaling as well as Treg development and function. Ssu72 deficiency impairs PLCγ1 downstream signaling and results in failure of Foxp3 induction. Thus, our studies show that the Ssu72-mediated cytokine response coordinates the differentiation and function of Treg cells in the periphery.

Ssu72 Dual-Specific Protein Phosphatase: From Gene to Diseases

More than 70% of eukaryotic proteins are regulated by phosphorylation. However, the mechanism of dephosphorylation that counteracts phosphorylation is less studied. Phosphatases are classified into 104 distinct groups based on substrate-specific features and the sequence homologies in their catalytic domains. Among them, dual-specificity phosphatases (DUSPs) that dephosphorylate both phosphoserine/threonine and phosphotyrosine are important for cellular homeostasis. Ssu72 is a newly studied phosphatase with dual specificity that can dephosphorylate both phosphoserine/threonine and phosphotyrosine. It is important for cell-growth signaling, metabolism, and immune activation. Ssu72 was initially identified as a phosphatase for the Ser5 and Ser7 residues of the C-terminal domain of RNA polymerase II. It prefers the cis configuration of the serine-proline motif within its substrate and regulates Pin1, different from other phosphatases. It has recently been reported that Ssu72 can regulate sister chromatid cohesion and the separation of duplicated chromosomes during the cell cycle. Furthermore, Ssu72 appears to be involved in the regulation of T cell receptor signaling, telomere regulation, and even hepatocyte homeostasis in response to a variety of stress and damage signals. In this review, we aim to summarize various functions of the Ssu72 phosphatase, their implications in diseases, and potential therapeutic indications.

Diverse and conserved roles of the protein Ssu72 in eukaryotes: from yeast to higher organisms

Gene transcription is a complex biological process that involves a set of factors, enzymes and nucleotides. Ssu72 plays a crucial role in every step of gene transcription. RNA polymerase II (RNAPII) occupies an important position in the synthesis of mRNAs. The largest subunit of RNAPII, Rpb1, harbors its C-terminal domain (CTD), which participates in the initiation, elongation and termination of transcription. The CTD consists of heptad repeats of the consensus motif Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7 and is highly conserved among different species. The CTD is flexible in structure and undergoes conformational changes in response to serine phosphorylation and proline isomerization, which are regulated by specific kinases/phosphatases and isomerases, respectively. Ssu72 is a CTD phosphatase with catalytic activity against phosphorylated Ser5 and Ser7. The isomerization of Pro6 affects the binding of Ssu72 to its substrate. Ssu72 can also indirectly change the phosphorylation status of Ser2. In addition, Ssu72 is a member of the 3'-end cleavage and polyadenylation factor (CPF) complex. Together with other CPF components, Ssu72 regulates the 3'-end processing of premature mRNA. Recent studies have revealed other roles of Ssu72, including its roles in balancing phosphate homeostasis and controlling chromosome behaviors, which should be further explored. In conclusion, the protein Ssu72 is an enzyme worthy of attention, not confined to its role in gene transcription.

Ssu72 regulates alveolar macrophage development and allergic airway inflammation by fine-tuning of GM-CSF receptor signaling

BACKGROUND

Fine-tuning of immune receptor signaling is critical for the development and functioning of immune cells. Moreover, GM-CSF receptor (GM-CSFR) signaling plays an essential role in the development of certain myeloid lineage cells, including alveolar macrophages (AMs). However, the significance of fine-tuning of GM-CSFR signaling in AMs and its relevance in allergic inflammation have not been reported.

OBJECTIVE

Our aim was to explore whether phosphatase Ssu72, originally identified as a regulator of RNA polymerase II activity, regulates AM development and allergic airway inflammation by regulating GM-CSF signaling.

METHODS

To address these issues, we generated LysM-CreSsu72^fl/fl and Cd11c-CreSsu72^fl/fl mice and used ovalbumin- or house dust mite-induced allergic asthma models.

RESULTS

Following GM-CSF stimulation, Ssu72 directly bound to the GM-CSFR β-chain in AMs, preventing phosphorylation. Consistently, mature Ssu72-deficient AMs showed higher phosphorylation of the GM-CSFR β-chain and downstream molecules, which resulted in greater dysregulation of cell cycle, cell death, cell turnover, mitochondria-related metabolism, and LPS responsiveness in AMs than in mature wild-type AMs. The dysregulation was restored by using a Janus kinase 2 inhibitor, which reduced GM-CSFR β-chain phosphorylation. LysM-CreSsu72^fl/fl mice exhibited deficits in development and maturation of AMs, which were also seen postnatally in Cd11c-CreSsu72^fl/fl mice. Furthermore, LysM-CreSsu72^fl/fl mice were less responsive to ovalbumin- or house dust mite-induced allergic asthma models than the control mice were; however, their responsiveness was restored by adoptive transfer of JAK2 inhibitor-pretreated mature Ssu72-deficient AMs.

CONCLUSION

Our results demonstrate that Ssu72 fine-tunes GM-CSFR signaling by both binding to and reducing phosphorylation of GM-CSFR β-chain, thereby regulating the development, maturation, and mitochondrial functions of AMs and allergic airway inflammation.

A Kinase-Phosphatase Network that Regulates Kinetochore-Microtubule Attachments and the SAC

The KMN network (for KNL1, MIS12 and NDC80 complexes) is a hub for signalling at the outer kinetochore. It integrates the activities of two kinases (MPS1 and Aurora B) and two phosphatases (PP1 and PP2A-B56) to regulate kinetochore-microtubule attachments and the spindle assembly checkpoint (SAC). We will first discuss each of these enzymes separately, to describe how they are regulated at kinetochores and why this is important for their primary function in controlling either microtubule attachments or the SAC. We will then discuss why inhibiting any one of them individually produces secondary effects on all the others. This cross-talk may help to explain why all enzymes have been linked to both processes, even though the direct evidence suggests they each control only one. This chapter therefore describes how a network of kinases and phosphatases work together to regulate two key mitotic processes.

The Extended Family of Protein Tyrosine Phosphatases

In higher eukaryotes, the Tyr phosphorylation status of cellular proteins results from the coordinated action of Protein Tyrosine Kinases (PTKs) and Protein Tyrosine Phosphatases (PTPs). PTPs have emerged as highly regulated enzymes with diverse substrate specificity, and proteins with Tyr-dephosphorylation or Tyr-dephosphorylation-like properties can be clustered as the PTPome. This includes proteins from the PTP superfamily, which display a Cys-based catalytic mechanism, as well as enzymes from other gene families (Asp-based phosphatases, His-based phosphatases) that have converged in protein Tyr-dephosphorylation-related functions by using non-Cys-based catalytic mechanisms. Within the Cys-based members of the PTPome, classical PTPs dephosphorylate specific phosphoTyr (pTyr) residues from protein substrates, whereas VH1-like dual-specificity PTPs dephosphorylate pTyr, pSer, and pThr residues, as well as nonproteinaceous substrates, including phosphoinositides and phosphorylated carbohydrates. In addition, several PTPs have impaired catalytic activity as a result of amino acid substitutions at their active sites, but retain regulatory functions related with pTyr signaling. As a result of their relevant biological activity, many PTPs are linked to human disease, including cancer, neurodevelopmental, and metabolic diseases, making these proteins important drug targets and molecular markers in the clinic. Here, a brief overview on the biochemistry and physiology of the different groups of proteins that belong to the mammalian PTPome is presented.

The Importance of Kinase-Phosphatase Integration: Lessons from Mitosis

Kinases and phosphatases work antagonistically to control the behaviour of individual substrate molecules. This can be incorrectly extrapolated to imply that they also work antagonistically on the signals or processes that these molecules control. In fact, in many situations kinases and phosphatases work together to positively drive signal responses. We explain how this 'cooperativity' is critical for setting the amplitude, localisation, timing, and shape of phosphorylation signals. We use mitosis to illustrate why these properties are important for controlling mitotic entry, sister chromatid cohesion, kinetochore-microtubule attachments, the spindle assembly checkpoint, mitotic spindle elongation, and mitotic exit. These examples provide a rationale to explain how complex signalling behaviour could rely on similar types of integration within many other biological processes.

Ssu72 attenuates autoimmune arthritis via targeting of STAT3 signaling and Th17 activation

Signal transducer and activator of transcription 3 (STAT3) orchestrates the differentiation of several cell types, including interleukin-17 (IL-17)-releasing Th17 cells. Dysregulation of Th17 cells results in chronic inflammatory responses. Ssu72 is a C-terminal domain phosphatase required for transcriptional regulation. However, the mechanism by which Ssu72 affects STAT3 activation and Th17 cell differentiation is unclear. Here, we found that Ssu72 overexpression suppresses STAT3 activation and Th17 cell responses in vitro. A systemic infusion of Ssu72 attenuates experimental autoimmune arthritis by reducing STAT3 activity and the differentiation of Th17 cells. It also reduces joint destruction, serum immunoglobulin concentrations and osteoclastogenesis but increases the number of marginal zone B cells and B10 cells. These effects are associated with reduced p-STAT3 levels and the suppression of Th17 cell formation in vivo. Based on these data, Ssu72 is related to STAT3 activation and the inflammatory response; and Ssu72 overexpression in T-cell-mediated immunity has potential utility for the treatment of autoimmune arthritis.

Protein Phosphatases Involved in Regulating Mitosis: Facts and Hypotheses

Almost all eukaryotic proteins are subject to post-translational modifications during mitosis and cell cycle, and in particular, reversible phosphorylation being a key event. The recent use of high-throughput experimental analyses has revealed that more than 70% of all eukaryotic proteins are regulated by phosphorylation; however, the mechanism of dephosphorylation, counteracting phosphorylation, is relatively unknown. Recent discoveries have shown that many of the protein phosphatases are involved in the temporal and spatial control of mitotic events, such as mitotic entry, mitotic spindle assembly, chromosome architecture changes and cohesion, and mitotic exit. This implies that certain phosphatases are tightly regulated for timely dephosphorylation of key mitotic phosphoproteins and are essential for control of various mitotic processes. This review describes the physiological and pathological roles of mitotic phosphatases, as well as the versatile role of various protein phosphatases in several mitotic events.

Oncogenic microtubule hyperacetylation through BEX4-mediated sirtuin 2 inhibition

Five brain-expressed X-linked (BEX) gene members (BEX1–5) are arranged in tandem on chromosome X, and are highly conserved across diverse species. However, little is known about the function and role of BEX. This study represents a first attempt to demonstrate the molecular details of a novel oncogene BEX4. Among BEX proteins, BEX4 localizes to microtubules and spindle poles, and interacts with α-tubulin (α-TUB) and sirtuin 2 (SIRT2). The overexpression of BEX4 leads to the hyperacetylation of α-TUB by inhibiting SIRT2-mediated deacetylation. Furthermore, we found BEX4 expression conferred resistance to apoptotic cell death but led to acquisition of aneuploidy, and also increased the proliferating potential and growth of tumors. These results suggest that BEX4 overexpression causes an imbalance between TUB acetylation and deacetylation by SIRT2 inhibition and induces oncogenic aneuploidy transformation.

Hepatocyte homeostasis for chromosome ploidization and liver function is regulated by Ssu72 protein phosphatase

Hepatocyte chromosome polyploidization is an important feature of liver development and seems to be required for response to liver stress and injury signals. However, the question of how polyploidization can be tightly regulated in liver growth remains to be answered. Using a conditional knockout mouse model, liver-specific depletion of Ssu72 protein phosphatase was found to result in impairment in regulation of polyploidization. Interestingly, the aberrant polyploidization in Ssu72-depleted mice was associated with impaired liver damage response and increased markers of liver injury and seemed to mimic the phenotypic features of liver diseases such as fibrosis, steatosis, and steatohepatitis. In addition, depletion of Ssu72 caused deregulation of cell cycle progression by overriding the restriction point of the cell cycle and aberrantly promoting DNA endoreplication through G2 /M arrest.

CONCLUSION

Ssu72 plays a substantial role in the maintenance of hepatic chromosome homeostasis and would allow monitoring of liver function.

The extended human PTPome: a growing tyrosine phosphatase family

Tyr phosphatases are, by definition, enzymes that dephosphorylate phospho-Tyr (pTyr) from proteins. This activity is found in several structurally diverse protein families, including the protein Tyr phosphatase (PTP), arsenate reductase, rhodanese, haloacid dehalogenase (HAD) and His phosphatase (HP) families. Most of these families include members with substrate specificity for non-pTyr substrates, such as phospho-Ser/phospho-Thr, phosphoinositides, phosphorylated carbohydrates, mRNAs, or inorganic moieties. A Cys is essential for catalysis in PTPs, rhodanese and arsenate reductase enzymes, whereas this work is performed by an Asp in HAD phosphatases and by a His in HPs, via a catalytic mechanism shared by all of the different families. The category that contains most Tyr phosphatases is the PTP family, which, although it received its name from this activity, includes Ser, Thr, inositide, carbohydrate and RNA phosphatases, as well as some inactive pseudophosphatase proteins. Here, we propose an extended collection of human Tyr phosphatases, which we call the extended human PTPome. The addition of new members (SACs, paladin, INPP4s, TMEM55s, SSU72, and acid phosphatases) to the currently categorized PTP group of enzymes means that the extended human PTPome contains up to 125 proteins, of which ~ 40 are selective for pTyr. We set criteria to ascribe proteins to the extended PTPome, and summarize the more important features of the new PTPome members in the context of their phosphatase activity and their relationship with human disease.

Regulation of the subcellular shuttling of Sgo1 between centromeres and chromosome arms by Aurora B-mediated phosphorylation

A minor fraction of cohesin complexes at chromosome arms is not removed by the prophase pathway, and maintained until metaphase and enriched at centromeres. Sgo1 localizes to chromosome arms from prophase to metaphase, and is indispensable for removing cohesin complexes from chromosome arms. However, it has not been established how the chromosome arm localization of Sgo1 leads to the establishment of cohesion on chromosomes. Here, we report that Aurora B kinase interacts with and phosphorylates Sgo1 in vitro and in vivo. Furthermore, the phosphorylation of Sgol by Aurora B kinase regulated the distribution of Sgo1 between centromeres and chromosome arms, and the expression of Aurora B kinase-dead mutants of Sgo1 caused mislocalization from centromeres to chromosome arms. These results suggest Aurora B kinase directly regulates the subcellular distribution of Sgo1 to facilitate the accurate separation of mitotic chromosomes.

CPF-associated phosphatase activity opposes condensin-mediated chromosome condensation

Functional links connecting gene transcription and condensin-mediated chromosome condensation have been established in species ranging from prokaryotes to vertebrates. However, the exact nature of these links remains misunderstood. Here we show in fission yeast that the 3′ end RNA processing factor Swd2.2, a component of the Cleavage and Polyadenylation Factor (CPF), is a negative regulator of condensin-mediated chromosome condensation. Lack of Swd2.2 does not affect the assembly of the CPF but reduces its association with chromatin. This causes only limited, context-dependent effects on gene expression and transcription termination. However, CPF-associated Swd2.2 is required for the association of Protein Phosphatase 1 PP1^Dis2 with chromatin, through an interaction with Ppn1, a protein that we identify as the fission yeast homologue of vertebrate PNUTS. We demonstrate that Swd2.2, Ppn1 and PP1^Dis2 form an independent module within the CPF, which provides an essential function in the absence of the CPF-associated Ssu72 phosphatase. We show that Ppn1 and Ssu72, like Swd2.2, are also negative regulators of condensin-mediated chromosome condensation. We conclude that Swd2.2 opposes condensin-mediated chromosome condensation by facilitating the function of the two CPF-associated phosphatases PP1 and Ssu72.

Failure to properly condense chromosomes prior to their segregation in mitosis can lead to genome instability. The evolutionary-conserved condensin complex is key to the condensation process but the molecular mechanisms underlying its localization pattern on chromosomes remain unclear. Previous observations showed that the localization of condensin is intimately linked to regions of high transcription, although, somewhat paradoxically, its association with chromatin is disrupted by a processive polymerase activity. Here we identify several RNA processing factors as negative regulators of condensin in fission yeast. Two of these factors associate with PP1 phosphatase as an independent entity within the Cleavage and Polyadenylation Factor (CPF), a complex key for 3′ end RNA processing. Lack of this module induces only minor and context-dependent effects on gene expression. Our data suggest that this module helps maintaining the proper level of phosphatase activity within the CPF and thereby opposes the function of condensin in mitotic chromosome condensation.