Copurification of casein kinase II with transcription factor ATF/E4TF3

Comparative analysis of type 2 diabetes-associated SNP alleles identifies allele-specific DNA-binding proteins for the KCNQ1 locus

Although recent genome-wide association studies (GWAS) have been extremely successful, it remains a big challenge to functionally annotate disease‑associated single nucleotide polymorphisms (SNPs), as the majority of these SNPs are located in non‑coding regions of the genome. In this study, we described a novel strategy for identifying the proteins that bind to the SNP‑containing locus in an allele‑specific manner and successfully applied this method to SNPs in the type 2 diabetes mellitus susceptibility gene, potassium voltage‑gated channel, KQT‑like subfamily Q, member 1 (KCNQ1). DNA fragments encompassing SNPs, and risk or non‑risk alleles were immobilized onto the novel nanobeads and DNA‑binding proteins were purified from the nuclear extracts of pancreatic β cells using these DNA‑immobilized nanobeads. Comparative analysis of the allele-specific DNA-binding proteins indicated that the affinities of several proteins for the examined SNPs differed between the alleles. Nuclear transcription factor Y (NF‑Y) specifically bound the non‑risk allele of the SNP rs2074196 region and stimulated the transcriptional activity of an artificial promoter containing SNP rs2074196 in an allele‑specific manner. These results suggest that SNP rs2074196 modulates the affinity of the locus for NF‑Y and possibly induces subsequent changes in gene expression. The findings of this study indicate that our comparative method using novel nanobeads is effective for the identification of allele‑specific DNA‑binding proteins, which may provide important clues for the functional impact of disease‑associated non‑coding SNPs.

Tools and methodologies capable of isolating and identifying a target molecule for a bioactive compound

Elucidating the mechanism of action of bioactive compounds, such as commonly used pharmaceutical drugs and biologically active natural products, in the cells and the living body is important in drug discovery research. To this end, isolation and identification of target protein(s) for the bioactive compound are essential in understanding its function fully. And, development of reliable tools and methodologies capable of addressing efficiently identification and characterization of the target proteins based on the bioactive compounds accelerates drug discovery research. Affinity-based isolation and identification of target molecules for the bioactive compounds is a classic, but still powerful approach. This paper introduces recent progress on affinity chromatography system, focusing on development of practical affinity matrices and useful affinity-based methodologies on target identification. Beneficial affinity chromatography systems with using practical tools and useful methodologies facilitate chemical biology and drug discovery research.

Preparation of conophylline affinity nano-beads and identification of a target protein

Conophylline, a vinca alkaloid extracted from the tropical plant Ervatamia microphylla, has been shown to induce the differentiation of insulin-producing beta-cells in cultured cells and in animals. However, its mechanism of action and the molecular target have remained unclear. Therefore, we prepared a fishing probe with conophylline to identify the target protein by using latex nano-beads, which are newly innovated tools for affinity-purification. With these conophylline-linked nano-beads, we found that conophylline directly interacted with ARL6IP. ARL6IP may thus be involved in the mechanism of cellular differentiation of beta-cells, and this probe should be useful to find other target proteins.

CK2-mediated phosphorylation of a type II regulatory subunit of cAMP-dependent protein kinase from the mollusk Mytilus galloprovincialis

Two isoforms of regulatory (R) subunit of cAMP-dependent protein kinase (PKA), named R(myt1) and R(myt2), were identified so far in the sea mussel Mytilus galloprovincialis. Out of them, only R(myt2) was phosphorylated in vitro by casein kinase 2 (CK2) using GTP as phosphate donor. CK2 catalytic subunit (CK2alpha) itself was sufficient to phosphorylate R(myt2), but phosphorylation was enhanced by the presence of the regulatory subunit CK2beta. Even in the absence of CK2, R(myt2) was phosphorylated to a certain extent when it was incubated with GTP. This basal phosphorylation was partially abolished by the known inhibitors apigenin and emodin, which suggests the presence of a residual amount of endogenous CK2 in the preparation of purified R subunit. CK2-mediated phosphorylation significantly decreases the ability of R(myt2) to inhibit PKA catalytic (C) subunit activity in the absence of cAMP. On the other hand, the sequence of several peptides obtained from the tryptic digestion of R(myt2) showed that mussel protein contains the signature sequence common to all PKA family members, within the "phosphate binding cassette" (PBC) A and B. Moreover, the degree of identity between the sequences of peptides from R(myt2), as a whole, and those from type II R subunits was 68-75%, but the global identity percentage with type I R subunits was only about 30%, so that R(myt2) can be classified as a type II R subunit.

Adeno-associated virus site-specific integration is regulated by TRP-185

Adeno-associated virus (AAV) integrates site specifically into the AAVS1 locus on human chromosome 19. Although recruitment of the AAV nonstructural protein Rep78/68 to the Rep binding site (RBS) on AAVS1 is thought to be an essential step, the mechanism of the site-specific integration, particularly, how the site of integration is determined, remains largely unknown. Here we describe the identification and characterization of a new cellular regulator of AAV site-specific integration. TAR RNA loop binding protein 185 (TRP-185), previously reported to associate with human immunodeficiency virus type 1 TAR RNA, binds to AAVS1 DNA. Our data suggest that TRP-185 suppresses AAV integration at the AAVS1 RBS and enhances AAV integration into a region downstream of the RBS. TRP-185 bound to Rep68 directly, changing the Rep68 DNA binding property and stimulating Rep68 helicase activity. We present a model in which TRP-185 changes the specificity of the AAV integration site from the RBS to a downstream region by acting as a molecular chaperone that promotes Rep68 complex formation competent for 3'-->5' DNA helicase activity.

H11 has dose-dependent and dual hypertrophic and proapoptotic functions in cardiac myocytes

We have shown previously that H11, a serine/threonine kinase, is up-regulated in a heart subjected to ischaemia/reperfusion. In the present study, we have characterized the cellular function of H11, using neonatal rat cardiac myocytes. Although transduction of adenovirus harbouring H11 at low doses increased the cell size, at higher doses it induced apoptosis in cardiac myocytes. Apoptosis was not observed when adenovirus harbouring H11-KI (kinase-inactive mutant of H11) was used, suggesting that the proapoptotic effect of H11 is kinase-dependent. The hypertrophic effect of H11 at high doses was unmasked when apoptosis was inhibited by the caspase inhibitor DEVD-CHO, suggesting that H11 stimulates both hypertrophy and apoptosis in parallel. H11-KI induced hypertrophy even at high doses, indicating that H11 stimulates hypertrophy through kinase-independent mechanisms. H11-KI activated Akt, and cardiac hypertrophy induced by H11-KI was blocked by LY294002, an inhibitor of phosphoinositide 3-kinase. Co-immunoprecipitation analyses indicated that H11 interacts with the alpha subunit of CK2 (casein kinase 2). Overexpression of H11 decreased the kinase activity of CK2. DRB (5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole), an inhibitor of CK2, mimicked the effect of H11, whereas DRB and H11 failed to exhibit additive effects on apoptosis, suggesting that H11 and DRB utilize a common mechanism to induce apoptosis, namely inhibition of CK2. In summary, H11 is a dual-function kinase in cardiac cells: it induces hypertrophy at low doses through kinase-independent activation of Akt, whereas it causes apoptosis at high doses through protein kinase-dependent mechanisms, in particular by physical interaction with and subsequent inhibition of CK2.

Phosphorylation of Epstein-Barr virus ZEBRA protein at its casein kinase 2 sites mediates its ability to repress activation of a viral lytic cycle late gene by Rta

ZEBRA, a member of the bZIP family, serves as a master switch between latent and lytic cycle Epstein-Barr virus (EBV) gene expression. ZEBRA influences the activity of another viral transactivator, Rta, in a gene-specific manner. Some early lytic cycle genes, such as BMRF1, are activated in synergy by ZEBRA and Rta. However, ZEBRA suppresses Rta's ability to activate a late gene, BLRF2. Here we show that this repressive activity is dependent on the phosphorylation state of ZEBRA. We find that two residues of ZEBRA, S167 and S173, that are phosphorylated by casein kinase 2 (CK2) in vitro are also phosphorylated in vivo. Inhibition of ZEBRA phosphorylation at the CK2 substrate motif, either by serine-to-alanine substitutions or by use of a specific inhibitor of CK2, abolished ZEBRA's capacity to repress Rta activation of the BLRF2 gene, but did not alter its ability to initiate the lytic cycle or to synergize with Rta in activation of the BMRF1 early-lytic-cycle gene. These studies illustrate how the phosphorylation state of a transcriptional activator can modulate its behavior as an activator or repressor of gene expression. Phosphorylation of ZEBRA at its CK2 sites is likely to play an essential role in proper temporal control of the EBV lytic life cycle.

Rep68 protein of adeno-associated virus type 2 interacts with 14-3-3 proteins depending on phosphorylation at serine 535

Rep78/68 proteins of adeno-associated virus type 2 (AAV-2) are involved in many aspects of the viral life cycle, including replication, gene expression, and site-specific integration. To understand the molecular mechanisms of the actions of Rep proteins, we searched for Rep68-interacting cellular proteins by utilizing a one-step affinity purification technique and identified two members of 14-3-3 proteins (14-3-3 epsilon and gamma). We found that phosphorylation of 535Ser at the carboxy terminus of Rep68 was critical for its association with 14-3-3. The association of 14-3-3 proteins to Rep68 resulted in reduction of the affinity of Rep68 for DNA. Furthermore, genome DNA replication of a recombinant mutant virus carrying a phosphorylation-deficient Rep68 (Ser535Ala) was more efficient than that of the wild-type virus. These results suggest that phosphorylation of Rep68 and subsequent association with 14-3-3 proteins regulates Rep-mediated functions during the AAV life cycle.

One-thousand-and-one substrates of protein kinase CK2?

CK2 (formerly termed "casein kinase 2") is a ubiquitous, highly pleiotropic and constitutively active Ser/Thr protein kinase whose implication in neoplasia, cell survival, and virus infection is supported by an increasing number of arguments. Here an updated inventory of 307 CK2 protein substrates is presented. More than one-third of these are implicated in gene expression and protein synthesis as being either transcriptional factors (60) or effectors of DNA/RNA structure (50) or translational elements. Also numerous are signaling proteins and proteins of viral origin or essential to virus life cycle. In comparison, only a minority of CK2 targets (a dozen or so) are classical metabolic enzymes. An analysis of 308 sites phosphorylated by CK2 highlights the paramount relevance of negatively charged side chains that are (by far) predominant over any other residues at positions n+3 (the most crucial one), n+1, and n+2. Based on this signature, it is predictable that proteins phosphorylated by CK2 are much more numerous than those identified to date, and it is possible that CK2 alone contributes to the generation of the eukaryotic phosphoproteome more so than any other individual protein kinase. The possibility that CK2 phosphosites play some global role, e.g., by destabilizing alpha helices, counteracting caspase cleavage, and generating adhesive motifs, will be discussed.

Identification and characterization of CKIP-1, a novel pleckstrin homology domain-containing protein that interacts with protein kinase CK2

The catalytic subunits of protein kinase CK2, CK2alpha and CK2alpha', are closely related to each other but exhibit functional specialization. To test the hypothesis that specific functions of CK2alpha and CK2alpha' are mediated by specific interaction partners, we used the yeast two-hybrid system to identify CK2alpha- or CK2alpha'-binding proteins. We report the identification and characterization of a novel CK2-interacting protein, designated CKIP-1, that interacts with CK2alpha, but not CK2alpha', in the yeast two-hybrid system. CKIP-1 also interacts with CK2alpha in vitro and is co-immunoprecipitated from cell extracts with epitope-tagged CK2alpha and an enhanced green fluorescent protein fusion protein encoding CKIP-1 (i.e. EGFP-CKIP-1) when they are co-expressed. CK2 activity is detected in anti-CKIP-1 immunoprecipitates performed with extracts from non-transfected cells indicating that CKIP-1 and CK2 interact under physiological conditions. The CKIP-1 cDNA is broadly expressed and encodes a protein with a predicted molecular weight of 46,000. EGFP-CKIP-1 is localized within the nucleus and at the plasma membrane. The plasma membrane localization is dependent on the presence of an amino-terminal pleckstrin homology domain. We postulate that CKIP-1 is a non-enzymatic regulator of one isoform of CK2 (i.e. CK2alpha) with a potential role in targeting CK2alpha to a particular cellular location.

Synergistic transcriptional activation by hGABP and select members of the activation transcription factor/cAMP response element-binding protein family

The Ets-related DNA-binding protein human GA-binding protein (hGABP) alpha interacts with the four ankyrin-type repeats of hGABPbeta to form an hGABP tetrameric complex that stimulates transcription through the adenovirus early 4 (E4) promoter. Using co-transfection assays, this study demonstrated that the hGABP complex mediated efficient activation of transcription from E4 promoter synergistically with activating transcription factor (ATF) 1 or cAMP response element-binding protein (CREB), but not ATF2/CRE-BP1. This synergy also partially occurred when hGABPalpha was used alone in place of the combination of hGABPalpha and hGABPbeta. hGABP activated an artificial promoter containing only ATF/CREB-binding sites under coexistence of ATF1 or CREB. Consistent with these results, physical interactions of hGABPalpha with ATF1 or CREB were observed in vitro. Functional domain analyses of the physical interactions revealed that the amino-terminal region of hGABPalpha bound to the DNA-binding domain of ATF1, which resulted in the formation of ternary complexes composed of ATF1, hGABPalpha, and hGABPbeta. In contrast to hGABPalpha, hGABPbeta did not significantly interact with ATF1 and CREB. Taken together, these results indicate that hGABP functionally interacts with selective members of the ATF/CREB family, and also suggest that synergy results from multiple interactions which mediate stabilization of large complexes within the regulatory elements of the promoter region, including DNA-binding and non-DNA-binding factors.

Protein kinase CK2 and its role in cellular proliferation, development and pathology

Protein kinase CK2 is a pleiotropic, ubiquitous and constitutively active protein kinase that can use both ATP and GTP as phosphoryl donors with specificity for serine/threonine residues in the vicinity of acidic amino acids. Recent results show that the enzyme is involved in transcription, signaling, proliferation and in various steps of development. The tetrameric holoenzyme (alpha2beta2) consists of two catalytic alpha-subunits and two regulatory beta-subunits. The structure of the catalytic subunit with the fixed positioning of the activation segment in the active conformation through its own aminoterminal region suggests a regulation at the transcriptional level making a regulation by second messengers unlikely. The high conservation of the catalytic subunit from yeast to man and its role in the tetrameric complex supports this notion. The regulatory beta-subunit has been far less conserved throughout evolution. Furthermore the existence of different CK2beta-related proteins together with the observation of deregulated CK2beta levels in tumor cells and the reported association of CK2beta protein with key proteins in signal transduction, e.g. A-Raf, Mos, pg90rsk etc. are suggestive for an additional physiological role of CK2beta protein beside being the regulatory compound in the tetrameric holoenzyme.

Phosphorylation of the DNA repair protein APE/REF-1 by CKII affects redox regulation of AP-1

The DNA repair protein apurinic endonuclease (APE/Ref-1) exerts several physiological functions such as cleavage of apurinic/apyrimidinic sites and redox regulation of the transcription factor AP-1, whose activation is part of the cellular response to DNA damaging treatments. Here we demonstrate that APE/Ref-1 is phosphorylated by casein kinase II (CKII). This was shown for both the recombinant APE/Ref-1 protein (Km=0.55 mM) and for APE/Ref-1 expressed in COS cells. Phosphorylation of APE/Ref-1 did not alter the repair activity of the enzyme, whereas it stimulated its redox capability towards AP-1, thus promoting DNA binding activity of AP-1. Inhibition of CKII mediated phosphorylation of APE/Ref-1 blocked mutagen-stimulated increase in AP-1 binding. It also abrogated the induction of c-Jun protein and rendered cells more sensitive to induced DNA damage. Thus, phosphorylation of APE/Ref-1 appears to be involved in regulating the different physiological activities of the enzyme. CKII mediated phosphorylation of APE/Ref-1 and concomitant increase in AP-1 binding activity appears to be a novel mechanism of cellular stress response, forcing transcription of AP-1 target gene(s) the product(s) of which may exert protective function.

Role of protein kinase CK2 in phosphorylation nucleosomal proteins in relation to transcriptional activity

Protein kinase CK2 undergoes rapid translocation to nuclear matrix and nucleosomes on androgenic stimulation of growth in prostatic epithelial cells. Further, CK2 appears to be regulated differentially in the transcriptionally active and inactive nucleosomes. We have investigated the role of CK2 in phosphorylation of nucleosome-associated proteins in the transcriptionally active and inactive nucleosomes that were isolated from ventral prostate subjected to different androgenic status in vivo. Proteins associated with these nucleosomes were phosphorylated via the intrinsic protein kinase activity, using [gamma-32P]ATP in the absence and presence of GTP. Several proteins appear to be potential substrates for CK2 associated with the nucleosomes. Among them are proteins that are differentially associated with the transcriptionally active and inactive nucleosomes. Phosphorylation of several of these proteins is modulated depending not only on their sites of association (i.e., active vs. inactive nucleosomes) but also on the state of transcriptional activity. Differential phosphorylation of specific proteins by CK2 associated with the active and inactive nucleosomes may be pertinent to the process of transcription regulation.

Evidence that P-TEFb alleviates the negative effect of DSIF on RNA polymerase II-dependent transcription in vitro

Recently, a positive and a negative elongation factor, implicated in 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibition of transcription elongation, has been identified. P-TEFb is a positive transcription elongation factor and the DRB-sensitive kinase that phosphorylates the C-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II). PITALRE, a member of the Cdc2 family of protein kinases, is the catalytic subunit of P-TEFb. DSIF is a human homolog of the yeast Spt4-Spt5 complex and renders elongation of transcription sensitive to DRB. DRB sensitivity-inducing factor (DSIF) binds to RNA Pol II and may directly regulate elongation. Here we show a functional interaction between P-TEFb and DSIF. The reduction of P-TEFb activity induced by either DRB, antibody against PITALRE, or immunodepletion resulted in a negative effect of DSIF on transcription. DSIF acts at an early phase of elongation, and the prior action of P-TEFb makes transcription resistant to DSIF. The state of phosphorylation of CTD determines the DSIF-RNA Pol II interaction, and may provide a direct link between P-TEFb and DSIF. Taken together, this study reveals a molecular basis for DRB action and suggests that P-TEFb stimulates elongation by alleviating the negative action of DSIF.

Casein kinase II interacts with the bZIP domains of several transcription factors

Casein kinase II (CKII) is thought to regulate a broad range of transcription factors, but its mode of action is not well characterized. We previously showed that CKII is co-purified with the ATF family of transcription factors using DNA-affinity latex beads. Here we report a functional and physical interaction between CKII and transcription factors. We demonstrate that CKII binds through its catalytic alpha and alpha' subunits to the basic leucine zipper (bZIP) DNA-binding domains of many transcription factors, including ATF1. Kinetic analysis using a surface plasmon resonance sensor suggests that CKII loosely associates with ATF1 in vivo . Deletion of the bZIP domain of ATF1 markedly reduces its phosphorylation by CKII, suggesting that the bZIP recruits CKII to the vicinity of the target site. ATF1-CKII complex is also formed on DNA. Using CKIIalpha fusedto a heterologous DNA-binding domain, we also demonstrate that CKII, when bound to DNA, efficiently phosphorylates its substrate, which is bound to the same DNA molecule. Taken together, CKII may regulate transcription (and possibly other events) by phosphorylating proteins on DNA.

Transcriptional factors for specific globin genes

Correct temporal control of the beta-like globin cluster is generated in part by the binding of tissue-restricted transcriptional regulators to their cognate sites. Erythroid Krüppel-like Factor (EKLF) is one of these red cell-specific activators that is particularly important for switching on adult beta-globin gene expression. However, its simple presence is not sufficient to activate the beta-globin promoter, as primitive erythroid cells and a number of erythroid cell lines express EKLF yet do not express adult beta-globin. One explanation that may account for these observations is that post-translational modification of EKLF differs within these cell populations. To address this issue, we are investigating whether phosphorylation plays a role in modulating EKLF activity. In vitro and in vivo approaches have been used to demonstrate that EKLF is a phosphoprotein whose ability to bind DNA and transcriptionally activate an adjacent promoter is critically dependent on its phosphorylation status. Of particular interest is a casein kinase II site within the EKLF minimal transactivation domain.

Dynamics of protein kinase CK2 association with nucleosomes in relation to transcriptional activity

Protein kinase CK2 has been implicated in control of cell growth and proliferation. Since growth stimuli evoke its preferential association with chromatin and nuclear matrix, we examined the dynamics of CK2 in nucleosomes fractionated on the basis of their transcriptional activity in the rat prostate. In this model, androgens induce expression of androgen-dependent genes but inhibit the androgen-repressed genes, whereas absence of androgens has the reverse effect. The level of CK2 was higher in the active than in inactive nucleosomes from normal prostate. Differential alterations in the levels of CK2 activity in the transcriptionally active versus inactive nucleosomes were evoked by androgen deprivation or administration. Comparison of the distribution of CK2 in active and inactive nucleosomes under varying androgenic conditions showed that the relative CK2 activity intrinsic to the transcriptionally active nucleosomes remained fairly stable, concordant with gene activity specific to the androgenic status. However, CK2 associated with inactive nucleosomes declined to a minimal level on androgen deprivation but increased rapidly on androgen administration (reflecting expression of multiple androgen-dependent genes). We suggest a role for CK2 in promoting the conformational transition of inactive nucleosomes to the active form and in the function of transcriptionally active nucleosomes.

Murine protein kinase CK2 alpha': cDNA and genomic cloning and chromosomal mapping

Protein kinase CK2 (casein kinase II) is a heterotetrameric enzyme implicated in many essential regulatory pathways in cells. We have determined the sequence of the murine CK2 alpha' cDNA that encodes a 350-amino-acid protein that would have 99 and 98% homology with the human and chicken proteins, respectively, and is also highly homologous to murine CK2 alpha. To clarify the sequence of the 5' end of the cDNA and to elucidate the structure and regulation of the gene, we obtained a bacterial artificial chromosome clone that contains the 35-kb CK2 alpha' gene. The gene consists of 12 small exons; the 5' end, including the first exon and intron, is extremely GC rich and contains a CpG island. The putative promoter contains potential binding sites for a variety of transcriptional factors but appears to lack CCAAT- or TATA-like elements. A polymorphic dinucleotide repeat in the fifth intron allowed us to map the CK2 alpha' gene to murine Chromosome 8.

DSIF, a novel transcription elongation factor that regulates RNA polymerase II processivity, is composed of human Spt4 and Spt5 homologs

We report the identification of a transcription elongation factor from HeLa cell nuclear extracts that causes pausing of RNA polymerase II (Pol II) in conjunction with the transcription inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB). This factor, termed DRB sensitivity-inducing factor (DSIF), is also required for transcription inhibition by H8. DSIF has been purified and is composed of 160-kD (p160) and 14-kD (p14) subunits. Isolation of a cDNA encoding DSIF p160 shows it to be a homolog of the Saccharomyces cerevisiae transcription factor Spt5. Recombinant Supt4h protein, the human homolog of yeast Spt4, is functionally equivalent to DSIF p14, indicating that DSIF is composed of the human homologs of Spt4 and Spt5. In addition to its negative role in elongation, DSIF is able to stimulate the rate of elongation by RNA Pol II in a reaction containing limiting concentrations of ribonucleoside triphosphates. A role for DSIF in transcription elongation is further supported by the fact that p160 has a region homologous to the bacterial elongation factor NusG. The combination of biochemical studies on DSIF and genetic analysis of Spt4 and Spt5 in yeast, also in this issue, indicates that DSIF associates with RNA Pol II and regulates its processivity in vitro and in vivo.

Two putative protein kinase CK2 phosphorylation sites are important for Myf-5 activity

Myf-5, a member of a family of muscle-specific transcription factors, is important for myogenic cell determination and differentiation. Here, we report that Myf-5 protein constitutes a substrate for phosphorylation in vitro by protein kinase CK2. We identified two potential phosphorylation sites at serine49 and serine133, both of which seem to be necessary for Myf-5 activity. Mutants which can no longer be phosphorylated fail to transactivate E-box-dependent reporter genes and act as trans-dominant repressors of wild-type Myf-5. Normal activity can be restored by replacing the serine residues with glutamate suggesting that a negative charge at these sites is obligatory for Myf-5 activity. Although serine133 is part of helix 2 which mediates dimerization, we find no evidence for impaired DNA-binding or heterodimerization of the Ser-Ala133 mutant. Some serine49 mutations exhibit reduced nuclear localization and/or protein stability. Our data suggest that CK2-mediated phosphorylation of Myf-5 is required for Myf-5 activity.

The nucleotidylylation of herpes simplex virus 1 regulatory protein alpha22 by human casein kinase II

The products of the alpha genes of herpes simplex virus 1, the infected cells proteins (ICP) 0, 4, 22, and 27 perform regulatory functions, are nucleotidylylated, and share the signaling or recognition sequence (RR(A/T)(P/S)R) that correctly predicted the nucleotidylylation of viral proteins encoded by UL21, UL31, UL49, and UL47 genes expressed later in infection. Extracts from uninfected HeLa cells or casein kinase II purified from sea star nucleotidylylated the ICP22 moiety of a glutathione S-transferase-ICP22 (GST22P) fusion protein with [alpha-32P]ATP or [2-3H]ATP. We report that: (i) Purified HeLa cell casein kinase II specifically labeled a glutathione S-transferase fusion protein containing the amino-terminal 151 amino acids of ICP22 with [2-3H]ATP. (ii) Nucleotidylylation of GST-ICP22 by purified enzyme exhibited positive cooperativity (Hill coefficient of 2 and a K' of 3.7 microM) and a Km = 37.7 microM for ATP. (iii) Nucleotidylylation was inhibited by heparin, casein, or ATPalphaS but not by ATPgammaS. (iv) Mutation of the signaling sequence from RRAPRR to LKAPEK abolished nucleotidylylation. We conclude that nucleotidylylation of proteins by casein kinase II requires the presence of the signaling or recognition sequence, involves the cleavage of the phosphodiester bond between the alpha and beta phosphate, and need not be preceded by phosphorylation.

Specific interaction between casein kinase 2 and the nucleolar protein Nopp140

Casein kinase 2 (CK2) is a multifunctional second messenger-independent protein serine/threonine kinase that phosphorylates many different proteins. To understand the function and regulation of this enzyme, biochemical methods were used to search for CK2-interacting proteins. Using immobilized glutathione S-transferase fusion proteins of CK2, the nucleolar protein Nopp140 was identified as a CK2-associated protein. It was found that Nopp140 binds primarily to the CK2 regulatory subunit, beta. The possible in vivo association of Nopp140 with CK2 was also suggested from a coimmunoprecipitation experiment in which Nopp140 was detected in immunoprecipitates of CK2 prepared from cell extracts. Further studies using an overlay technique with radiolabeled CK2 as a probe revealed a direct CK2-Nopp140 interaction. Using deletion mutants of CK2beta subunits, the binding region of the CK2beta subunit to Nopp140 has been mapped. It was found that the NH2-terminal 20 amino acids of CK2beta are involved. Since Nopp140 has been identified as a nuclear localization sequence-binding protein and has been shown to shuttle between the cytoplasm and the nucleus, the finding of a CK2-Nopp140 interaction could shed light on our understanding of the function and regulation of CK2 and Nopp140.