Protein kinase and specific phosphate acceptor proteins associated with tupaia herpesvirus

Open reading frames encoding a protein kinase, homolog of glycoprotein gX of pseudorabies virus, and a novel glycoprotein map within the unique short segment of equine herpesvirus type 1

DNA sequence analysis of the unique short (Us) segment of the genome of equine herpesvirus type 1 Kentucky A strain (EHV-1) by our laboratory and strains Kentucky D and AB1 by other workers identifies a total of nine open reading frames (ORF). In this report, we present the DNA sequence of three of these newly identified ORFs, designated EUS 2, EUS 3, and EUS 4. The EUS 2 ORF is 1146 nucleotides (nt) in length and encodes a potential protein of 382 amino acids. Cis-regulatory sequences upstream of the putative ATG start codon include a G/C box 112 nt upstream and two potential TATA-like elements located between 15 and 90 nt before the ATG. The EUS 2 translation product exhibits significant homology to Ser/Thr protein kinases encoded within the Us segments of other herpesviruses, such as herpes simplex virus (26% homology) and pseudorabies virus (PRV), (45% homology), and possesses sequence domains conserved in protein kinases of cellular and viral origin. The EUS 3 ORF begins 127 nt downstream from the EUS 2 stop codon and ends at a stop codon 1119 nt further downstream. A single TATA-like element maps 61 nt upstream of the ORF. This ORF encodes a potential protein of 373 amino acids and is a homolog of glycoprotein gX of PRV, as judged by overall homology of amino acid residues, cysteine displacement, and presence of potential glycosylation sites and signal sequence. Interestingly, the EUS 4 ORF encodes a potential membrane glycoprotein that does not exhibit homology to any reported protein sequence. The EUS 4 ORF encodes a 383 amino acid polypeptide with a sequence indicative of a signal sequence at its amino terminal end, glycosylation sites for N-linked oligosaccharides, and a transmembrane domain near its carboxyl terminus. Several cis-acting regulatory sequences lie upstream of this ORF. These findings support the observation that the short region of alphaherpesviruses show considerable variation in their genetic content and gene organization.

Identification of new protein kinase-related genes in three herpesviruses, herpes simplex virus, varicella-zoster virus, and Epstein-Barr virus

By using amino acid sequence patterns (motifs) diagnostic of conserved regions within the catalytic domains of protein kinases, homologous open reading frames of three herpesviruses were identified as protein kinase-related genes. The three sequences, herpes simplex virus gene UL13, varicella-zoster virus gene 47, and Epstein-Barr virus gene BGLF4, resemble serine/threonine kinases rather than tyrosine kinases.

Properties of poliovirus associated protein kinase

Highly purified virulent poliovirus preparations harbour an endogenous protein kinase. Enzyme activity increases significantly upon purification of infectious virus particles from infected HeLa cells. Enzyme activity is stimulated by divalent cations. The substrate specificity and the degree of stimulation of the kinase are dependent on the nature of the divalent cations included in the assay. The preferred substrates for this kinase are the viral capsid proteins. Exogenously added proteins such as alpha-casein, phosvitin and protamine are also phosphorylated by the kinase. Moreover, these proteins enhance the phosphorylation of viral proteins. In the presence of Mg++ VP 2 and VP 0 are highly phosphorylated, while in the presence of Zn++ only VP 2 and VP 4, but not VP 0 or exogenous proteins are phosphorylated. Poliovirus associated protein kinase exhibits optimal activity at pH 7.9 in the presence of 10 mM Mg++. The Km for ATP is shown to be 40 microM. By testing different nucleotides as phosphate donors a specificity of the phosphorylation reaction for ATP is demonstrated. Phosphoamino acid analysis of hydrolysates of the substrates phosphorylated in the presence of Mg++ by thin layer electrochromatography and HPLC yielded phosphoserine and phosphothreonine from viral capsid proteins while hydrolysates of protamine yield only phosphoserine. Destabilization of the viral capsid, e.g. by preincubation at 42 degrees C for 20 minutes results in a stimulation of kinase activity. Moreover, phosphorylation of the poliovirus capsid proteins itself results in destabilization of the viral capsid. These findings suggest that phosphorylation of the viral coat proteins triggers or enhances the uncoating of poliovirus leading to the release of viral RNA.

Varicella zoster virus glycoprotein gpI is selectively phosphorylated by a virus-induced protein kinase

Varicella zoster virus glycoprotein I (VZV gpI; Mr 98,000) was phosphorylated in virus-infected human cell monolayers, while two other major VZV glycoproteins (gpII and gpIII) were not similarly modified. Phosphorylation of VZV gpI was not blocked by inhibitors of glycosylation, nor were the phosphoryl groups enzymatically removed by endoglycosidases. Phosphoamino acid analysis revealed the presence of phosphoserine and phosphothreonine residues on the polypeptide backbone. The selective nature of the phosphorylation event was further demonstrated in vitro by a protein kinase (Mr 50,000), which was present in virus-infected cells but absent from uninfected cells or purified virions. The enzyme catalyzed the transfer of 32Pi from [gamma-32P]ATP to gpI but not to gpII and gpIII. Like VZV gpI, this virus-induced protein kinase was also a constituent of the plasma membrane of live VZV-infected cells.

Characterization of phosphoproteins and protein kinase activity of virions, noninfectious enveloped particles, and dense bodies of human cytomegalovirus

Phosphorylation of the proteins of human cytomegalovirus (CMV) virions, noninfectious enveloped particles (NIEPs), and dense bodies was investigated. Analyses of particles phosphorylated in vivo showed the following. Virions contain three predominant phosphoproteins (i.e., basic phosphoprotein and upper and lower matrix proteins) and at least nine minor phosphorylated species. NIEPs contain all of these and one additional major species, the assembly protein. Dense bodies contain only one (i.e., lower matrix) of the predominant and four of the minor virion phosphoproteins. Two-dimensional (charge-size) separations in denaturing polyacrylamide gels showed that the relative net charges of the predominant phosphorylated species ranged from the basic phosphoprotein to the more neutral upper matrix protein. In vitro assays showed that purified virions of human CMV have an associated protein kinase activity. The activity was detected only after disrupting the envelope; it had a pH optimum of approximately 9 to 9.5 and required a divalent cation, preferring magnesium to manganese. In vitro, this activity catalyzed phosphorylation of the virion proteins observed to be phosphorylated in vivo. Peptide comparisons indicated that the sites phosphorylated in vitro are a subset of those phosphorylated in vivo, underscoring the probable biological relevance of the kinase activity. Casein, phosvitin, and to a minor extent lysine-rich histones served as exogenous phosphate acceptors. Arginine-rich and lysine-rich histones and protamine sulfate, as well as the polyamines spermine and spermidine, stimulated incorporation of phosphate into the endogenous viral proteins. Virions of all human and simian CMV strains tested showed this activity. Analyses of other virus particles, including three intracellular capsid forms (i.e., A, B, and C capsids), NIEPs, and dense bodies, indicated that the active enzyme was not present in the capsid. Rate-velocity sedimentation of disrupted virions separated the protein kinase activity into two fractions: one that phosphorylated exogenous casein and another that phosphorylated primarily the endogenous virion proteins.

Partial purification and characterization of a new phosphoprotein kinase from cells infected with pseudorabies virus

Cytoplasmic fractions from normal baby hamster kidney fibroblasts and from fibroblasts infected with pseudorabies virus were fractionated by DEAE-cellulose chromatography and fractions assayed for protein kinase activity. In preparations from uninfected and infected cells protein kinase activities identified as casein kinase I and II, the two isoforms of the cyclic-AMP-dependent protein kinase, protein kinase C, and a presumed proteolytic fragment of protein kinase C were present in comparable amounts. However in infected cells a new protein kinase activity was detected, appearing about 4 h after infection and increasing during the following 6 h at least. This new protein kinase was purified 100-fold by high-performance gel-permeation and ion-exchange chromatography, and characterized. It has an apparent relative molecular mass of 68 000 on the basis of gel-permeation chromatography, and a sedimentation coefficient of 4.3 S. It catalysed the phosphorylation of serine residues of basic proteins in vitro, with protamine a better substrate than mixed histones; and used ATP (apparent Km = 60 microM), but not GTP, as phosphoryl donor. Molecules that can serve as effectors for other protein kinases (cyclic AMP, cyclic GMP, Ca2+ + calmodulin, Ca2+ + phospholipid, double-stranded RNA, and heparin) did not significantly alter the activity of this enzyme. A distinguishing characteristic of the protein kinase was a high KCl concentration optimum with the persistence of activity up to 800 mM KCl, at least.

Molecular cloning and physical mapping of the tupaia herpesvirus genome

Purified virion DNA of about 200 kilobase pairs of tupaia herpesvirus strain 2 was cleaved with EcoRI or HindIII restriction endonuclease. Restriction fragments representing the complete viral genome including both termini were inserted into the EcoRI, HindIII, and EcoRI-HindIII sites of the bacterial plasmid pAT153. Restriction maps for the restriction endonucleases EcoRI and HindIII were constructed with data derived from Southern blot hybridizations of individual viral DNA fragments or cloned DNA fragments which were hybridized to either viral genome fragments or recombinant plasmids. The analysis revealed that the tupaia herpesvirus genome consists of a long unique sequence of 200 kilobase pairs and that inverted repeat DNA sequences of greater than 40 base pairs do not occur, in agreement with previous electron microscopic data. No DNA sequence homology was detectable between the tupaia herpesvirus DNA and the genome of murine cytomegalovirus, which was reported to have a similar structure. In addition, seven individual isolates of tupaia herpesvirus were characterized. The isolates can be grouped into five strains by their DNA cleavage patterns.