[Show abstract][Hide abstract] ABSTRACT: Drosophila Enhancer of split M8, an effector of Notch signaling, is regulated by protein kinase CK2. The phosphatase PP2A is thought to play an opposing (inhibitory) role, but the identity of the regulatory subunit was unknown. The studies described here reveal a role for the PP2A regulatory subunit widerborst (wdb) in three developmental contexts; the bristle, wing and the R8 photoreceptors of the eye. wdb overexpression elicits bristle and wing defects akin to reduced Notch signaling, whereas hypomorphic mutations in this PP2A subunit elicit opposite effects. We have also evaluated wdb functions using mutations in Notch and E(spl) that affect the eye. We find that the eye and R8 defects of the well-known Nspl mutation are enhanced by a hypomorphic allele of wdb, whereas they are strongly rescued by wdb overexpression. Similarly, ectopic wdb rescues the eye and R8 defects of the E(spl)D mutation, which affects the m8 gene. In addition, wdb overexpression also rescues the bristle defects of ectopically expressed M8, or the eye and R8 defects of its CK2 phosphomimetic variant M8-S159D. The latter finding suggests that PP2A may target M8 at highly conserved residues in the vicinity of the CK2 site, whose phosphorylation controls repression of Atonal and the R8 fate. Together, the studies identify PP2A-Wdb as a participant in Notch signaling, and suggest that M8 activity is controlled by phosphorylation and dephosphorylation. The conservation of the phosphorylation sites between Drosophila E(spl) and the HES/HER proteins from mammals, reptiles, amphibians, birds and fish raises the prospect that this mode of regulation is widespread.
PLoS ONE 01/2014; 9(7):e101884. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CK2 is a Ser/Thr protein kinase that regulates the activity of the Drosophila basic-helix-loop-helix (bHLH) repressor M8 encoded by the Enhancer of split Complex (E(spl)C) during neurogenesis. Specifically, phosphorylation appears to elicit a conformational change in an autoinhibited state of M8 to one that is permissive for repression. We describe biochemical and molecular modeling studies that provide new insights into repression by M8. Our studies implicate the phosphorylation domain in autoinhibition, and indicate that binding of the co-repressor Groucho (Gro) is context-dependent. Molecular modeling indicates that the Orange domain, proposed to be a specificity-determinant, may instead play a structural role, and that a conformational rearrangement of this domain may be necessary for repression. This model also provides a structural mechanism for the behavior of mutant alleles of the m8 gene. The insights gained from these studies should be applicable to the conserved metazoan bHLH repressors of the Hairy and Enhancer of Split (HES) family that are related to Drosophila M8.
Molecular and Cellular Biochemistry 07/2011; 356(1-2):217-25. · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Analysis of the retinal defects of a CK2 phosphomimetic variant of E(spl)M8 (M8S(159)D) and the truncated protein M8* encoded by the E(spl)D allele, suggest that the nonphosphorylated CtD "autoinhibits" repression. We have investigated this model by testing for inhibition (in "trans") by the CtD fragment in its nonphosphorylated (M8-CtD) and phosphomimetic (M8SD-CtD) states. In N(+) flies, ectopic M8-CtD compromises lateral inhibition, i.e., elicits supernumerary bristles as with loss of N signaling. This antimorphic activity of M8-CtD strongly rescues the reduced eye and/or bristle loss phenotypes that are elicited by ectopic M8SD or wild type M8. Additionally, the severely reduced eye of N(spl)/Y; E(spl)D/+ flies is also rescued by M8-CtD. Rescue is specific to the time and place, the morphogenetic furrow, where "founding" R8 photoreceptors are specified. In contrast, the phosphomimetic M8SD-CtD that is predicted to be deficient for autoinhibition, exhibits significantly attenuated or negligible activity. These studies provide evidence that autoinhibition by the CtD regulates M8 activity in a phosphorylation-dependent manner.
[Show abstract][Hide abstract] ABSTRACT: Repression by E(spl)M8 during inhibitory Notch (N) signaling (lateral inhibition) is regulated, in part, by protein kinase CK2, but the involvement of a phosphatase has been unclear. The studies we report here employ Tik, a unique dominant-negative (DN) mutation in the catalytic subunit of CK2, in a Gal4-UAS based assay for impaired lateral inhibition. Specifically, overexpression of Tik elicits ectopic bristles in N(+) flies and suppresses the retinal defects of the gain-of-function allele N(spl). Functional dissection of the two substitutions in Tik (M(161)K and E(165)D), suggests that both mutations contribute to its DN effects. While the former replacement compromises CK2 activity by impairing ATP-binding, the latter affects a conserved motif implicated in binding the phosphatase PP2A. Accordingly, overexpression of microtubule star (mts), the PP2A catalytic subunit closely mimics the phenotypic effects of loss of CK2 functions in N(+) or N(spl) flies, and elicits notched wings, a characteristic of N mutations. Our findings suggest antagonistic roles for CK2 and PP2A during inhibitory N signaling.
[Show abstract][Hide abstract] ABSTRACT: Our results, using endogenous mutants and Gal4-UAS driven transgenes, implicate multisite phosphorylation in repression by E(spl)M8. We propose that these phosphorylations occur in the morphogenetic furrow (MF) to reverse an auto-inhibited state of M8, enabling repression of Atonal during R8 specification. Our studies address the paradoxical behavior of M8*, the truncated protein encoded by E(spl)D. We suggest that differences in N signaling in the bristle versus the eye underlie the antimorphic activity of M8* in N(+) (ectopic bristles) and hypermorphic activity in N(spl) (reduced eye). Ectopic M8* impairs eye development (in N(spl)) only during establishment of the atonal feedback loop (anterior to the MF), but is ineffective after this time point. In contrast, a CK2 phosphomimetic M8 lacking Groucho (Gro) binding, M8SDDeltaGro, acts antimorphic in N(+) and suppresses the eye/R8 and bristle defects of N(spl), as does reduced dosage of E(spl) or CK2. Multisite phosphorylation could serve as a checkpoint to enable a precise onset of repression, and this is bypassed in M8*. Additional implications are discussed.
[Show abstract][Hide abstract] ABSTRACT: CK2 is a Ser/Thr protein kinase essential for animal development. Although null alleles for CK2 are available in the mouse and Drosophila models, they are lethal when homozygous, thus necessitating conditional alleles for analysis of its developmental roles. We describe the isolation of temperature-sensitive (ts) alleles of Drosophila CK2alpha (dCK2alpha). These alleles efficiently rescue lethality of yeast lacking endogenous CK2 at 29 degrees C, but this ability is lost at higher temperatures in an allele-specific manner. These ts-variants exhibit properties akin to the wild type protein, and interact robustly with dCK2beta. Modeling of these ts-variants using the crystal structure of human CK2alpha indicates that the affected residues are in close proximity to the active site. We find that substitution of Asp(212) elicits potent ts-behavior, an important finding because this residue contributes to stability of the activation segment and is invariant in other Ser/Thr protein kinases.
Molecular and Cellular Biochemistry 12/2008; 323(1-2):49-60. · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hairy is a repressor that regulates bristle patterning, and its loss elicits ectopic bristles (neural hyperplasia). However, it has remained unknown whether Hairy is regulated by phosphorylation. We describe here the interaction of protein kinase CK2 and Hairy. Hairy is robustly phosphorylated by the CK2-holoenzyme (CK2-HoloE) purified from Drosophila embryos, but weakly by the catalytic CK2alpha-subunit alone, suggesting that this interaction requires the regulatory CK2beta-subunit. Consistent with this, Hairy preferentially forms a direct complex with CK2-HoloE. Importantly, we demonstrate genetic interactions between CK2 and hairy (h). Thus, flies trans-heterozygous for alleles of CK2alpha and h display neural hyperplasia akin to homozygous hypomorphic h alleles. In addition, we show that similar phenotypes are elicited in wild-type flies upon expression of RNAi constructs against CK2alpha/beta, and that these defects are sensitive to h gene dosage. Together, these studies suggest that CK2 contributes to repression by Hairy.
Biochemical and Biophysical Research Communications 08/2008; 373(4):637-42. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lateral inhibition is critical for cell fate determination and involves the functions of Notch (N) and its effectors, the Enhancer of Split Complex, E(spl)C repressors. Although E(spl) proteins mediate the repressive effects of N in diverse contexts, the role of phosphorylation was unclear. The studies we describe implicate a common role for the highly conserved Ser/Thr protein kinase CK2 during eye and bristle development. Compromising the functions of the catalytic (alpha) subunit of CK2 elicits a rough eye and defects in the interommatidial bristles (IOBs). These phenotypes are exacerbated by mutations in CK2 and suppressed by an increase in the dosage of this protein kinase. The appearance of the rough eye correlates, in time and space, to the specification and refinement of the 'founding' R8 photoreceptor. Consistent with this observation, compromising CK2 elicits supernumerary R8's at the posterior margin of the morphogenetic furrow (MF), a phenotype characteristic of loss of E(spl)C and impaired lateral inhibition. We also show that compromising CK2 elicits ectopic and split bristles. The former reflects the specification of excess bristle SOPs, while the latter suggests roles during asymmetric divisions that drive morphogenesis of this sensory organ. In addition, these phenotypes are exacerbated by mutations in CK2 or E(spl), indicating genetic interactions between these two loci. Given the centrality of E(spl) to the repressive effects of N, our studies suggest conserved roles for this protein kinase during lateral inhibition. Candidates for this regulation are the E(spl) repressors, the terminal effectors of this pathway.
Mechanisms of Development 10/2006; 123(9):649-64. · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The yeast two-hybrid (Y2H)1 system (1) has revolution- ized the identiWcation of protein-protein interactions and has had a tremendous impact on cell and developmental biology. In the Y2H system, two proteins are expressed as fusions with the DNA-binding domain (DB) of Gal4/LexA, the bait, and a transcription activation domain (AD), the prey. Interactions between the bait and the prey reconsti- tute a functional transcription factor that activates reporter genes that have been made responsive to binding by Gal4/ LexA (reviewed in Refs. (2,3)). Since its initial development, the Y2H system has undergone many modiWcations, each of which has enabled unique applications. These adapta- tions include an array of DB and AD fusion vectors for expression of varying levels or types of fusion proteins, the use of multiple baits and reporters that enable simultaneous tests for speciWcity, the one- and three-hybrid systems to identify DNA-binding proteins and ternary interactions, and so forth. Although these adaptations have reWned this approach, they do not enable discrimination of physiologi- cal targets of protein kinases that has generally required downstream biochemistry to conWrm whether the interact- ing protein is also a target for phosphorylation. This last step is often rate limiting because it requires phosphoryla- tion of recombinant proteins or peptides by puriWed kinase(s). Our laboratory has employed the Y2H system exten- sively to identify physiological partners of CK2, a con- served Ser/Thr protein kinase from the fruit Xy, Drosophila (4-7). Such screens, using the catalytic () subunit of CK2, have identiWed an array of developmentally important proteins. Analysis of the primary sequences of these pro- teins for the CK2 consensus site, (S/T)-(D/E/x)-x-(D/E), indicated that some of these were likely to be targets for phosphorylation, and this subsequently was conWrmed via biochemistry. One of these studies involved the interactions
[Show abstract][Hide abstract] ABSTRACT: Drosophila Groucho, like its vertebrate Transducin-like Enhancer-of-split homologues, is a corepressor that silences gene expression in numerous developmental settings. Groucho itself does not bind DNA but is recruited to target promoters by associating with a large number of DNA-binding negative transcriptional regulators. These repressors tether Groucho via short conserved polypeptide sequences, of which two have been defined. First, WRPW and related tetrapeptide motifs have been well characterized in several repressors. Second, a motif termed Engrailed homology 1 (eh1) has been found predominantly in homeodomain-containing transcription factors. Here we describe a yeast two-hybrid screen that uncovered physical interactions between Groucho and transcription factors, containing eh1 motifs, with different types of DNA-binding domains. We show that one of these, the zinc finger protein Odd-skipped, requires its eh1-like sequence for repressing specific target genes in segmentation. Comparison between diverse eh1 motifs reveals a bias for the phosphoacceptor amino acids serine and threonine at a fixed position, and a mutational analysis of Odd-skipped indicates that these residues are critical for efficient interactions with Groucho and for repression in vivo. Our data suggest that phosphorylation of these phosphomeric residues, if it occurs, will down-regulate Groucho binding and therefore repression, providing a mechanism for posttranslational control of Groucho-mediated repression.
Molecular and Cellular Biology 01/2006; 25(24):10711-20. · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In Drosophila, protein kinase CK2 regulates a diverse array of developmental processes. One of these is cell-fate specification (neurogenesis) wherein CK2 regulates basic-helix-loop-helix (bHLH) repressors encoded by the Enhancer of Split Complex (E(spl)C). Specifically, CK2 phosphorylates and activates repressor functions of E(spl)M8 during eye development. In this study we describe the interaction of CK2 with an E(spl)-related bHLH repressor, Deadpan (Dpn). Unlike E(spl)-repressors which are expressed in cells destined for a non-neural cell fate, Dpn is expressed in the neuronal cells and is thought to control the activity of proneural genes. Dpn also regulates sex-determination by repressing sxl, the primary gene involved in sex differentiation. We demonstrate that Dpn is weakly phosphorylated by monomeric CK2alpha, whereas it is robustly phosphorylated by the embryo-holoenzyme, suggesting a positive role for CK2beta. The weak phosphorylation by CK2alpha is markedly stimulated by the activator polylysine to levels comparable to those with the holoenzyme. In addition, pull down assays indicate a direct interaction between Dpn and CK2. This is the first demonstration that Dpn is a partner and target of CK2, and raises the possibility that its repressor functions might also be regulated by phosphorylation.
Molecular and Cellular Biochemistry 07/2005; 274(1-2):133-9. · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Notch effector E(spl)M8 is phosphorylated at Ser159 by CK2, a highly conserved Ser/Thr protein kinase. We have used the Gal4-UAS system to assess the role of M8 phosphorylation during bristle and eye morphogenesis by employing a non-phosphorylatable variant (M8SA) or one predicted to mimic the 'constitutively' phosphorylated protein (M8SD). We find that phosphorylation of M8 does not appear to be critical during bristle morphogenesis. In contrast, only M8SD elicits a severe 'reduced eye' phenotype when it is expressed in the morphogenetic furrow of the eye disc. M8SD elicits neural hypoplasia in eye discs, elicits loss of phase-shifted Atonal-positive cells, i.e. the 'founding' R8 photoreceptors, and consequently leads to apoptosis. The ommatidial phenotype of M8SD is similar to that in Nspl/Y; E(spl)D/+ flies. E(spl)D, an allele of m8, encodes a truncated protein known as M8*, which, unlike wild type M8, displays exacerbated antagonism of Atonal via direct protein-protein interactions. In line with this, we find that the M8SD-Atonal interaction appears indistinguishable from that of M8*-Atonal, whereas interaction of M8 or M8SA appears marginal, at best. These results raise the possibility that phosphorylation of M8 (at Ser159) might be required for its ability to mediate 'lateral inhibition' within proneural clusters in the developing retina. This is the first identification of a dominant allele encoding a phosphorylation-site variant of an E(spl) protein. Our studies uncover a novel functional domain that is conserved amongst a subset of E(spl)/Hes repressors in Drosophila and mammals, and suggests a potential role for CK2 during retinal patterning.
Mechanisms of Development 04/2004; 121(3):273-86. · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reports that estrogen treatment modulates arachidonic acid metabolism by bone and bone cells are found in the literature. However, conflicting indications of the relationship that exists between estrogen and arachidonic acid metabolism emerge from the analysis of those reports. The present studies were undertaken to determine if estrogen effected the production of prostaglandins (PG) in human osteoblast-like (hOB) cell cultures derived from adults, under basal or cytokine-stimulated conditions. A 48-hour estrogen pretreatment did not modify hOB cell PG biosynthesis on a qualitative basis, and PGE2 formation predominated under all tested conditions. Estrogen pretreatment did lead to increased PGE2 production in specimens stimulated conjointly with transforming growth factor-beta1 and tumor necrosis factor-alpha ( p < 0.001). No changes in PGE2 production were observed in estrogen pretreated specimens stimulated singly with either tested cytokine, nor in samples in which either TGFbeta or TNF was replaced by interleukin-1beta. Anti-estrogen (ICI 164,384) inclusion prevented the estrogen-dependent increase in PGE2 production in the TGFbeta plus TNF-stimulated samples. These results suggest that an estrogen effect on bone cell prostaglandin biosynthesis may be most evident and significant under conditions in which the cells are exposed to multiple osteotropic cytokines, a condition that applies during the bone remodeling process.
Calcified Tissue International 01/2004; 73(6):565-74. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Drosophila melanogaster casein kinase II (CKII) is composed of catalytic alpha and regulatory beta subunits that generate the alpha2beta2 holoenzyme. A two-hybrid screen of a Drosophila embryo library using CKIIalpha as bait has resulted in the isolation of multiple cDNAs encoding SSL, a CKIIbeta-like polypeptide. We demonstrate that CKIIbeta, beta', and SSL exhibit robust and comparable interaction with CKIIalpha. Residues in SSL that mediate interaction with CKIIalpha appear similar to those in CKIIbeta, and SSL forms homodimers and heterodimers with CKIIbeta or beta' as well. We have tested all known Drosophila CKIIbeta-like proteins for rescue of the ion-homeostasis defect of yeast lacking beta subunits and find that CKIIbeta and SSL complement, beta' has marginal function, and Stellate appears non-functional. We have used real-time RT-PCR to assess developmental expression, and find that CKIIbeta is robust and ubiquitous, whereas SSL is restricted to males (third-instar-larvae, pupae, and adults), but is nondetectable in females of the corresponding stages. These results indicate that SSL expression encompasses a greater developmental window than that previously suggested and may confer distinct functions to CKII in a sex-specific manner.
Biochemical and Biophysical Research Communications 03/2003; 301(4):941-7. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ubiquitous eukaryotic protein kinase CKII (casein kinase II) has been found to interact with a number of cellular proteins, either through the catalytic subunit or the regulatory subunit. Using the yeast two-hybrid screening method, we found that the catalytic subunit of Drosophila melanogaster CKII (DmCKII) interacts with Drosophila ribosomal protein L22 (rpL22). This interaction was also observed in vitro with a glutathione-S-transferase (GST)-rpL22 fusion protein. The predicted full-length Drosophila rpL22 protein has an N-terminal extension rich in alanine, lysine, and proline that appears to be unique to Drosophila. Deletion mapping revealed that the conserved core of rpL22 is responsible for the interaction with CKII. Moreover, purified DmCKII can phosphorylate a GST-L22 fusion protein at the C-terminal end, suggesting that this protein may be a substrate of CKII in Drosophila.
Biochemical and Biophysical Research Communications 11/2002; 298(1):60-6. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Drosophila melanogaster protein kinase CK2 (DmCK2) is a Ser/Thr protein kinase composed of catalytic alpha and regulatory beta subunits associated as an alpha2beta2 heterotetramer. Using the two hybrid system, we have screened a Drosophila embryo cDNA library in order to identify proteins that interact with DmCK2alpha. One of these cDNAs encodes a novel previously undescribed zinc-finger protein, which we call ZFP47. ZFP47 interacts with DmCK2alpha but not with DmCK2beta, indicating that this interaction is specific for the catalytic subunit of CK2. In situ hybridization to polytene chromosomes indicates that the corresponding gene is located at the 72A interval of chromosome III. Sequence analysis indicates that ZFP47 contains a consensus site for phosphorylation by CK2, 4 C1H1-type zinc-fingers, and a bipartite nuclear localization signal. Consistent with the prediction of a site for phosphorylation by CK2, we demonstrate that ZFP47 is phosphorylated by CK2 purified from Drosophila embryos. These studies demonstrate that ZFP47 is a new physiological partner and substrate of CK2.
Molecular and Cellular Biochemistry 12/2001; 227(1-2):99-105. · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: D. melanogaster CK2 (DmCK2) is a highly conserved protein kinase that is composed of catalytic, alpha, and regulatory, beta, subunits associated as an alpha2beta2 heterotetramer. In order to analyze the functions of CK2 in this metazoan model, we have used the two hybrid approach to identify interacting proteins. One of these cDNAs, DmA24, encodes a novel polypeptide with no homologs in GenBank, and is notable in that it contains a bipartite nuclear localization signal and two sites for phosphorylation by CK2. In situ hybridization to polytene chromosomes indicates that the DmA24 gene is located at the 61 D interval of chromosome II a region that also harbors 3 additional genes with similar structure. DmA24p interacts with DmCK2alpha, but not with DmCK2beta, demonstrating that this interaction is specific for the catalytic subunit of CK2. In addition, the protein is phosphorylated by the holoenzyme purified from Drosophila embryos. These studies identify DmA24p as a potentially new physiological partner of DmCK2. In addition, we also report the results of a large-scale screen that has identified a new set of DmCK2-interacting proteins. Most notable among these are Surf6, a nucleolar protein involved in RNA processing, and Spalt, a homeotic protein.
Molecular and Cellular Biochemistry 12/2001; 227(1-2):91-8. · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Drosophila melanogaster casein kinase II (DmCKII) is composed of catalytic (alpha) and regulatory (beta) subunits associated as an alpha2beta2 heterotetramer. Using the two-hybrid system, we have screened a D. melanogaster embryo cDNA library for proteins that interact with DmCKIIalpha. One of the cDNAs isolated in this screen encodes m7, a basic helix-loop-helix (bHLH)-type transcription factor encoded by the Enhancer of split complex (E(spl)C), which regulates neurogenesis. m7 interacts with DmCKIIalpha but not with DmCKIIbeta, suggesting that this interaction is specific for the catalytic subunit of DmCKII. In addition to m7, we demonstrate that DmCKIIalpha also interacts with two other E(spl)C-derived bHLH proteins, m5 and m8, but not with other members, such as m3 and mC. Consistent with the specificity observed for the interaction of DmCKIIalpha with these bHLH proteins, sequence alignment suggests that only m5, m7, and m8 contain a consensus site for phosphorylation by CKII within a subdomain unique to these three proteins. Accordingly, these three proteins are phosphorylated by DmCKIIalpha, as well as by the alpha2beta2 holoenzyme purified from Drosophila embryos. In line with the prediction of a single consensus site for CKII, replacement of Ser(159) of m8 with either Ala or Asp abolishes phosphorylation, identifying this residue as the site of phosphorylation. We also demonstrate that m8 forms a direct physical complex with purified DmCKII, corroborating the observed two-hybrid interaction between these proteins. Finally, substitution of Ser(159) of m8 with Ala attenuates interaction with DmCKIIalpha, whereas substitution with Asp abolishes the interaction. These studies constitute the first demonstration that DmCKII interacts with and phosphorylates m5, m7, and m8 and suggest a biochemical and/or structural basis for the functional equivalency of these bHLH proteins that is observed in the context of neurogenesis.
Journal of Biological Chemistry 02/2001; 276(3):2159-67. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Drosophila melanogaster casein kinase II (CKII) is composed of catalytic alpha and regulatory beta subunits. Using the two-hybrid system, we have isolated a number of cDNAs that are related to a previously published cDNA encoding the beta subunit, but exhibit divergent 5' sequences. To determine the source of this sequence variation, we have isolated the gene encoding the beta subunit of CKII. The beta gene contains five exons encompassing the complete open reading frame, as well as five alternative exons in the 5' untranslated region (UTR). Only one 5' UTR exon is contained in each cDNA, implying five distinct classes of transcript. In addition, the beta gene contains at least two poly(A) addition signals which generate additional complexity at the 3' end. The complex pattern of transcription may serve a role in the spatial and/or temporal expression of the beta subunit since, with one exception, all transcripts encode the full-length beta polypeptide. Phylogenetic comparison of the beta genes of Drosophila, C. elegans, and mammals reveals three invariant introns as well as evidence of recent intron gain/loss.
Molecular Cell Biology Research Communications 06/2000; 3(5):283-91.
[Show abstract][Hide abstract] ABSTRACT: Drosophila melanogaster casein kinase II (DmCKII) is composed of catalytic alpha and regulatory beta subunits associated as an alpha2beta2 heterotetramer. Using the two-hybrid system, we have screened a Drosophila embryo cDNA library for proteins that interact with DmCKII alpha. One of the cDNAs encodes a novel beta-like polypeptide, which we designate beta'. In situ hybridization localizes the corresponding gene to 56F1-2, a site distinct from that of both the beta gene and the Stellate family of beta-like sequences. The predicted sequence of beta' is more closely related to the beta subunit of Drosophila and other metazoans than to the Stellate family of proteins, suggesting that it is a second regulatory subunit. In vitro reconstitution studies show that a GST-beta' fusion protein associates with the alpha subunit to generate a tetrameric complex with regulatory properties similar to those of the native alpha2beta2 holoenzyme. The data are consistent with the proposed role of the beta' subunit as an integral component of the holoenzyme.
Molecular Cell Biology Research Communications 05/1999; 1(1):21-8.