The 140-kDa RR1 protein from both HSV-1 and HSV-2 contains an intrinsic protein kinase activity capable of autophosphorylation but it is transphosphorylation defective

Herpes simplex virus type 2 growth and latency reactivation by cocultivation are inhibited with antisense oligonucleotides complementary to the translation initiation site of the large subunit of ribonucleotide reductase (RR1)

Antisense oligonucleotides complementary to the translation initiation site of the herpes simplex virus type 2 (HSV-2) large subunit of ribonucleotide reductase (RR1) were studied for their ability to inhibit RR1 expression, HSV-2 growth, and its reactivation from latently infected ganglia. The oligomers caused a significant decrease (90%-97% inhibition) in HSV-2 RR1 expression and inhibited HSV-2 growth, with IC50 and IC90 values of 0.11 and 1.0 microM, respectively. The titers of HSV-2 mutants that are respectively deleted in the PK (ICP10deltaPK) or RR (ICP10deltaRR) domains of RR1 were also significantly (500-20,000-fold) decreased, indicating that the antisense oligomers interfere with the independent contributions of the two RR1 functions (PK and RR) toward virus growth. Inhibition was sequence specific, as evidenced by the failure of a two-base mutant (RR1TImu) to inhibit protein expression and HSV-2 growth. Furthermore, the antisense oligomers inhibited HSV-2 reactivation by cocultivation of latently infected ganglia (0/8). Virus was reactivated from ganglia cultured without oligomers, in the presence of unrelated oligomers (6/8), or in the presence of the two-base mutant RR1TImu (5/8) (p < 0.007 by two-tailed Fisher exact test). HSV-2 growth was not inhibited by antisense oligonucleotides complementary to the splice junction of HSV-2 immediate-early (IE) pre-mRNA 4 and 5 (IE4,5SA) or the translation initiation site of IE mRNA 4 (IE4TI), although the respective HSV-1-specific oligomers inhibit HSV-1 growth.

The R1 subunit of herpes simplex virus ribonucleotide reductase is a good substrate for host cell protein kinases but is not itself a protein kinase

The N terminus of the R1 subunit of herpes simplex virus type 2 ribonucleotide reductase is believed to be a protein kinase domain mainly because the R1 protein was phosphorylated in a protein kinase assay on blot. Using Escherichia coli and adenovirus expression vectors to produce R1, we found that, whereas the reductase activity of both recombinant proteins was similar, efficient phosphorylation of R1 and casein in the presence of Mg2+ was obtained only with the R1 purified from eukaryotic cells. Phosphorylation of this R1, in solution or on blot, results mainly from the activity of casein kinase II (CKII), a co-purifying protein kinase. Labeling on blot occurs from CKII leakage off the membrane and its subsequent high affinity binding to in vivo CKII-phosphorylated R1. CKII target sites were mapped to an acidic serine-rich segment of the R1 N terminus. Improvement in purification of the R1 expressed in eukaryotic cells nearly completely abolished its phosphorylation potential. An extremely low level of phosphorylation observed in the presence of Mn2+ with the R1 produced in E. coli was probably due to an unidentified prokaryotic protein kinase. These results provide evidence that the herpes simplex virus type 2 R1 does not possess an intrinsic protein kinase activity.

The large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) is associated with the virion tegument and has PK activity

The large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) was identified in sucrose gradient-purified HSV-2 virions by immunoprecipitation/immunoblotting with antibody specific for the protein kinase (PK) domain. Immunoblotting of individual gradient fractions indicated that ICP10 cosediments with the major capsid protein and the highest virus titers. ICP10 was not labeled by iodination of purified virions, indicating that it is not located on the virion surface. After envelope glycoproteins were removed by detergent treatment, ICP10 was associated with capsid-tegument particles and became sensitive to trypsin digestion. The capsid-tegument-associated ICP10 was phosphorylated and had PK activity in vitro and on Immobilon membranes. A mutant ICP10 protein deleted in the PK domain (p95) was also associated with purified virions (ICP10deltaPK virus) but it lacked PK activity. The data indicate that ICP10 is contained within the tegument component where it retains intrinsic PK activity.

Herpes simplex virus DNA replication

The Herpesviridae comprise a large class of animal viruses of considerable public health importance. Of the Herpesviridae, replication of herpes simplex virustype-1 (HSV-1) has been the most extensively studied. The linear 152-kbp HSV-1 genome contains three origins of DNA replication and approximately 75 open-reading frames. Of these frames, seven encode proteins that are required for originspecific DNA replication. These proteins include a processive heterodimeric DNA polymerase, a single-strand DNA-binding protein, a heterotrimeric primosome with 5'-3' DNA helicase and primase activities, and an origin-binding protein with 3'-5' DNA helicase activity. HSV-1 also encodes a set of enzymes involved in nucleotide metabolism that are not required for viral replication in cultured cells. These enzymes include a deoxyuridine triphosphatase, a ribonucleotide reductase, a thymidine kinase, an alkaline endo-exonuclease, and a uracil-DNA glycosylase. Host enzymes, notably DNA polymerase alpha-primase, DNA ligase I, and topoisomerase II, are probably also required. Following circularization of the linear viral genome, DNA replication very likely proceeds in two phases: an initial phase of theta replication, initiated at one or more of the origins, followed by a rolling-circle mode of replication. The latter generates concatemers that are cleaved and packaged into infectious viral particles. The rolling-circle phase of HSV-1 DNA replication has been reconstituted in vitro by a complex containing several of the HSV-1 encoded DNA replication enzymes. Reconstitution of the theta phase has thus far eluded workers in the field and remains a challenge for the future.