Class-switched memory B cells remodel BCRs within secondary germinal centers

Effective vaccines induce high-affinity memory B cells and durable antibody responses through accelerated mechanisms of natural selection. Secondary changes in antibody repertoires after vaccine boosts suggest progressive rediversification of B cell receptors (BCRs), but the underlying mechanisms remain unresolved. Here, the integrated specificity and function of individual memory B cell progeny revealed ongoing evolution of polyclonal antibody specificities through germinal center (GC)-specific transcriptional activity. At the clonal and subclonal levels, single-cell expression of the genes encoding the costimulatory molecule CD83 and the DNA polymerase Polη segregated the secondary GC transcriptional program into four stages that regulated divergent mechanisms of memory BCR evolution. Our studies demonstrate that vaccine boosts reactivate a cyclic program of GC function in class-switched memory B cells to remodel existing antibody specificities and enhance durable immunological protection.

Antiviral treatment of chronic hepatitis B virus infection. I. Changes in viral markers with interferon combined with adenine arabinoside

Twenty patients with chronic active hepatitis and 12 patients with chronic persistent hepatitis associated with hepatitis B virus (HBV) infection were treated with human leukocyte interferon or adenine arabinoside alone or in combination. With interferon alone, four of 16 patients showed a permanent disappearance of HBV-associated DNA polymerase (DNAP) activity from serum. Of six patients treated with adenine arabinoside alone, only one patient became permanently DNAP-negative. With a regimen of multiple cycles of combined interferon and adenine arabinoside, seven of 16 male patients became permanently DNAP-negative. Of 69 patients who met the criteria for admission to the program, spontaneous decreases in DNAP activity without treatment were observed in only 9% during a mean observation period of 10 months. In general, patients with chronic active hepatitis, those who are female, and those with a history of recent steroid therapy responded to the antiviral agents significantly better than did the other patients.

Anti-influenza virus cytotoxic T lymphocytes recognize the three viral polymerases and a nonstructural protein: responsiveness to individual viral antigens is major histocompatibility complex controlled

It has recently been shown that antiviral major histocompatibility complex class I-restricted cytotoxic T lymphocytes can recognize proteins that serve as internal viral structural components (influenza A virus nucleoprotein, vesicular stomatitis virus nucleocapsid protein). To further examine the role of internal viral proteins in cytotoxic T-lymphocyte recognition, we constructed recombinant vaccinia viruses containing individual influenza A virus genes encoding three viral polymerases (PB1, PB2, PA) and a protein not incorporated into virions (NS1). We found that cells infected with each of these recombinant vaccinia viruses could be lysed by anti-influenza cytotoxic T lymphocytes. Cytotoxic T-lymphocyte responsiveness to the individual viral antigens varied greatly between mouse strains. By using congenic mouse strains, responsiveness to PB1 and PB2 was found to cosegregate with major histocompatibility complex haplotype. These findings provide further evidence that internal antigens play a critical role in cytotoxic T-lymphocyte recognition of virus-infected cells. Additionally, they suggest that the cytotoxic T-lymphocyte response to viral antigens may often be restricted to only a fraction of the major histocompatibility complex class I repertoire.

Cutting edge: DNA polymerases mu and lambda are dispensable for Ig gene hypermutation

Mutations arising in Ig V genes during an immune response are most likely introduced by one or several error-prone DNA polymerases. Many of the recently described nonreplicative DNA polymerases have an intrinsic fidelity compatible with such an activity, the strongest candidates being polymerase (pol) eta, pol iota, pol zeta, and pol mu. We report in this work that mice inactivated for either of the two polymerases related to pol beta (i.e., pol mu and pol lambda) are viable and fertile and display a normal hypermutation pattern.

Expression, purification, and initial kinetic characterization of the large subunit of the human mitochondrial DNA polymerase

Faulty replication of the human mitochondrial genome is thought to be the cause of many diseases; moreover, the low selectivity of the mitochondrial DNA polymerase has been implicated as the cause of many side effects observed in the treatment of viral infections such as HIV. To better understand how the mitochondrial genome is replicated, we cloned a cDNA encoding the large subunit of human DNA polymerase gamma, the enzyme that replicates the mitochondrial genome. The large subunit was recombinantly expressed and purified to near homogeneity. The purified enzyme demonstrated both polymerase and 3'-5' exonuclease activity. The purified protein was examined in single nucleotide incorporation assays, demonstrating that the enzyme had a maximum polymerization rate of 3.5 s-1 and a dissociation rate from the DNA substrate of 0.03 s-1, affording a calculated processivity of 116. The dissociation constants for the enzyme binding to DNA and nucleoside triphosphate were 39 nM and 14 microM, respectively. The 3'-5' exonuclease rate was measured at 0. 18 s-1. Though the slow rate of polymerization suggests that the large subunit of human DNA polymerase gamma may require accessory factors to increase its processivity of polymerization, the kinetic parameters indicate that the large subunit of DNA polymerase gamma could replicate the mitochondrial genome in a physiologically relevant time frame. This study provides the initial characterization of the large subunit of DNA polymerase gamma and establishes the baseline for examination of the effects of accessory proteins such as the putative small subunit.

Autoantibody to the proliferating cell nuclear antigen neutralizes the activity of the auxiliary protein for DNA polymerase delta

Two murine monoclonal antibodies to the proliferating cell nuclear antigen (PCNA), a rabbit anti-N-terminal peptide antibody and human auto-antibody to PCNA reacted with the auxiliary protein for DNA polymerase delta from fetal calf thymus following SDS-polyacrylamide gel electrophoresis, confirming the identity of PCNA and the auxiliary protein. Undenatured auxiliary protein was immunoprecipitated by the human autoantibody, but not by the monoclonal antibodies, which were raised to SDS-denatured PCNA, nor by the anti-N-terminal peptide antibody, suggesting that the epitopes recognized by both the monoclonal antibodies and the anti-peptide antibody are not exposed in the native protein. The human anti-PCNA autoantibody neutralized the activity of the auxiliary protein for DNA polymerase delta, but did not inhibit the activity of pol delta itself. The ability of pol delta to utilize template/primers containing long stretches of single-stranded template was inhibited by the anti-PCNA autoantibody, whereas the activity of pol alpha on such templates was not affected, confirming the specificity of the auxiliary protein for pol delta. The ability of PCNA, a cell cycle-regulated protein, to regulate the activity of pol delta suggests a central role for pol delta in cellular DNA replication.

Infection of human B cells with Epstein-Barr virus results in the expression of somatic hypermutation-inducing molecules and in the accrual of oncogene mutations

Infection of human B cells with Epstein-Barr virus (EBV) was seen to result in activation-induced cytidine deaminase (AID) and polymerase-eta (pol-eta) gene expression. AID and pol-eta are cellular gene products that play central roles in the DNA-modifying processes involved in immunoglobulin gene class switch recombination and somatic hypermutation. Errors in these processes can result in oncogene mutation/translocation, thereby contributing to lymphomagenesis. It was seen that EBV infected, AID, and pol-eta expressing B cells accumulated mutations in cellular proto-oncogenes (BCL-6 and p53) that are known to be involved in the genesis of B cell lymphoma. The nature of the mutations seen in these oncogenes was consistent with the known activity of AID and pol-eta. These findings indicate that EBV induced AID and pol-eta expression, and that this was associated with oncogene mutation, providing a novel means by which EBV infection of B cells may contribute to lymphomagenesis.

Functional interaction between Epstein-Barr virus DNA polymerase catalytic subunit and its accessory subunit in vitro

The Epstein-Barr virus (EBV) DNA polymerase catalytic subunit (BALF5 protein) and its accessory subunit (BMRF1 protein) have been independently overexpressed and purified (T. Tsurumi, A. Kobayashi, K. Tamai, T. Daikoku, R. Kurachi, and Y. Nishiyama, J. Virol. 67:4651-4658, 1993; T. Tsurumi, J. Virol. 67:1681-1687, 1993). In an investigation of the molecular basis of protein-protein interactions between the subunits of the EBV DNA polymerase holoenzyme, we compared the DNA polymerase activity catalyzed by the BALF5 protein in the presence or absence of the BMRF1 polymerase accessory subunit in vitro. The DNA polymerase activity of the BALF5 polymerase catalytic subunit alone was sensitive to high ionic strength on an activated DNA template (80% inhibition at 100 mM ammonium sulfate). Addition of the polymerase accessory subunit to the reaction greatly enhanced DNA polymerase activity in the presence of high concentrations of ammonium sulfate (10-fold stimulation at 100 mM ammonium sulfate). Optimal stimulation was obtained when the molar ratio of BMRF1 protein to BALF5 protein was 2 or more. The DNA polymerase activity of the BALF5 protein along with the BMRF1 protein was neutralized by a monoclonal antibody to the BMRF1 protein, whereas that of the BALF5 protein alone was not, suggesting a specific interaction between the BALF5 protein and the BMRF1 protein in the reaction. The processivity of nucleotide polymerization of the BALF5 polymerase catalytic subunit on singly primed M13 single-stranded DNA circles was low (approximately 50 nucleotides). Addition of the BMRF1 polymerase accessory subunit resulted in a strikingly high processive mode of deoxynucleotide polymerization (> 7,200 nucleotides). These findings strongly suggest that the BMRF1 polymerase accessory subunit stabilizes interaction between the EBV DNA polymerase and primer template and functions as a sliding clamp at the growing 3'-OH end of the primer terminus to increase the processivity of polymerization.

Antibodies as thermolabile switches: high temperature triggering for the polymerase chain reaction

We demonstrate the utility of antibodies to the DNA polymerase from Thermus aquaticus (TaqPol) as thermolabile inhibitors of TaqPol activity. One of the limitations of the polymerase chain reaction (PCR) is the co-amplification of non-specific products caused by TaqPol activity on low stringency templates present in the initial cycle of PCR. We have used anti-TaqPol antibodies as thermolabile switches that inhibit TaqPol activity at low temperatures (20-40 degrees C) and release fully active TaqPol when they are inactivated by elevated temperatures in the PCR thermal cycling (70-98 degrees C). Several in a set of high affinity anti-TaqPol monoclonal antibodies fully inhibited TaqPol activity at 37 degrees C. The capacity for inhibition was ablated by incubation at temperatures high enough to denature antibodies but not sufficiently high to significantly reduce TaqPol activity. In a PCR model system, preincubation of TaqPol with these antibodies yielded PCR product consisting entirely of the intended product and the absence or significant reduction of non-specific products and primer dimers. In evaluation of clinical samples such antibody triggering yielded defined PCR product and higher sensitivity because of the absence of non-specific products.

Effect of DNA polymerase inhibitors on DNA repair in intact and permeable human fibroblasts: evidence that DNA polymerases delta and beta are involved in DNA repair synthesis induced by N-methyl-N'-nitro-N-nitrosoguanidine

The involvement of DNA polymerases alpha, beta, and delta in DNA repair synthesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was investigated in human fibroblasts (HF). The effects of anti-(DNA polymerase alpha) monoclonal antibody, (p-n-butylphenyl)deoxyguanosine triphosphate (BuPdGTP), dideoxythymidine triphosphate (ddTTP), and aphidicolin on MNNG-induced DNA repair synthesis were investigated to dissect the roles of the different DNA polymerases. A subcellular system (permeable cells), in which DNA repair synthesis and DNA replication were differentiated by CsCl gradient centrifugation of BrdUMP density-labeled DNA, was used to examine the effects of the polymerase inhibitors. Another approach investigated the effects of several of these inhibitors on MNNG-induced DNA repair synthesis in intact cells by measuring the amount of [3H]thymidine incorporated into repaired DNA as determined by autoradiography and quantitation with an automated video image analysis system. In permeable cells, MNNG-induced DNA repair synthesis was inhibited 56% by 50 micrograms of aphidicolin/mL, 6% by 10 microM BuPdGTP, 13% by anti-(DNA polymerase alpha) monoclonal antibodies, and 29% by ddTTP. In intact cells, MNNG-induced DNA repair synthesis was inhibited 57% by 50 micrograms of aphidicolin/mL and was not significantly inhibited by microinjecting anti-(DNA polymerase alpha) antibodies into HF nuclei. These results indicate that both DNA polymerases delta and beta are involved in repairing DNA damage caused by MNNG.

Comparison of cytotoxic T lymphocyte responses induced by peptide or DNA immunization: implications on immunogenicity and immunodominance

To study the mechanisms that influence the immunogenicity and immunodominance of potential cytotoxic T lymphocyte (CTL) epitopes, we conducted a systematic analysis of the CTL response raised in HLA-A*0201/Kb (A2/Kb) transgenic mice against the viral antigen, hepatitis B virus polymerase (HBV pol). From a pool of 26 nonamer peptides containing the HLA-A*0201-binding motif, we selected A2-binding peptides, immunized A2/Kb animals, and tested the CTL raised against the peptide for recognition of HBV pol transfectants. Of nine immunogenic CTL epitopes, only four were recognized on HBV pol transfectants, whereas the other five were cryptic. Characterization of the peptide-specific CTL lines indicated that crypticity may result from either poor processing or low T cell receptor (TCR) avidity. To identify the immunodominant epitopes, we determined the CTL specificities induced in A2/Kb animals in response to priming with HBV pol cDNA. We obtained a response against three epitopes that were contained with the set of four epitopes recognized by peptide-specific CTL on HBV pol transfectants. Comparative analysis of cDNA priming and peptide priming revealed, therefore, the presence of a subdominant epitope. We conclude that for the HBV pol antigen, the repertoire of CTL specificities is shaped by major histocompatibility complex class I peptide binding capacity, antigen processing, and TCR availability.

Characterization and application to hot start PCR of neutralizing monoclonal antibodies against KOD DNA polymerase

DNA polymerase from Pyrococcus kodakaraensis KOD1 (KOD DNA polymerase) is one of the most efficient thermostable PCR enzymes exhibiting higher accuracy and elongation velocity than any other commercially available DNA polymerase [M. Takagi et al. (1997) Appl. Environ. Microbiol. 63, 4504-4510]. However, even when KOD DNA polymerase was used for PCR, troubles with nonspecific DNA amplification and primer dimer formation still remain because of undesirable DNA polymerase activity during the first denaturing step of PCR. In order to inhibit this undesirable DNA polymerase activity (hot start PCR), two neutralizing monoclonal antibodies (mAbs), 3G8 and betaG1, to KOD DNA polymerase were obtained. Both of these antibodies belong to subclass IgG(1), <font face="k">k. K(d) values were 7.3 x 10(-8) for 3G8 and 1.1 x 10(-6) for betaG1. Nucleotide sequencing of cDNAs of these monoclonal antibodies revealed their sequences to differ in their CDRs (complementarity determining region). Exonuclease activity measurement and epitope mapping revealed that the epitope for 3G8 is located in conserved regions among alpha-like (family B) DNA polymerases (Region II), and the epitope for betaG1 is located in the 3'-5' exonuclease domain. When hot start PCR with each of these mAbs was performed, the specificity of target gene amplification became much higher than in reactions without monoclonal antibody. Furthermore, this method can easily be applied to long distance PCR (>17.5 kbp).

Diagnosis of nasopharyngeal carcinoma by means of recombinant Epstein-Barr virus proteins

The immune response of patients with nasopharyngeal carcinoma to Epstein-Barr virus (EBV) antigens is diagnostic of the tumour. Existing tests use EBV antigens produced in EBV-infected lymphoblastoid cells, but the virus replicates poorly in these cells. Serum samples from 18 patients diagnosed as having nasopharyngeal carcinoma were screened by western blot analysis, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence tests for antibodies to the EBV-coded alkaline deoxyribonuclease (DNase), thymidine kinase, and membrane antigen (gp340/220) produced in recombinant baculovirus or bovine papillomavirus systems. Each protein was a useful diagnostic marker for nasopharyngeal carcinoma, although in the gp340/220 ELISAs there was substantial overlap for both IgG and IgA antibodies between serum samples from nasopharyngeal carcinoma patients and those from healthy donors seropositive for EBV. The EBV thymidine kinase was the most sensitive predictor of nasopharyngeal carcinoma; all such samples showed both IgG and IgA antibody responses to this protein and all gave clearly distinct titres from those of the EBV-seropositive donors in the IgA test. Each of the recombinant systems described is suitable for use in large-scale screening programmes for the early diagnosis of nasopharyngeal carcinoma.

Purification, biochemical characterization and serological analysis of cellular deoxyribonucleic acid polymerases and a reverse transcriptase from spleen of a patient with myelofibrotic syndrome

The present study describes the separation and purification of a reverse transcriptase and cellular DNA polymerases from the human spleen of a patient with myelofibrotic syndrome. The specific requirements with respect to bivalent cations and template-primers for DNA polymerase-alpha, DNA polymerase-beta and DNA polymerase-gamma, as well as for the reverse transcriptase, are reported. Sedimentation-velocity measurements of the purified enzymes gave values of 150000, 40000, 100000 and 70000 daltons for DNA polymerase-alpha DNA polymerase-beta, DNA polymerase-gamma and the reverse transcriptase respectively. Serological studies have shown that the reverse transcriptase from human spleen is not antigenically related to cellular DNA polymerase-alpha, -beta or -gamma, but is antigenically related to reverse transcriptase from simian sarcoma virus and gibbon-ape leukaemia virus.

Production and characterization of monoclonal antibody against 10S DNA polymerase alpha from calf thymus

One hybridoma cell line that produces an antibody directed against 10S DNA polymerase alpha purified from calf thymus was obtained. The monoclonality of the antibody was tested by sodium dodecyl sulfate polyacrylamide gel electrophoresis, isoelectrofocusing and antibody subclass determination. The antibody specifically recognized the 10S DNA polymerase alpha and 6.5S DNA polymerase alpha-2 from calf thymus, but not 6.5S DNA polymerase alpha-1. The antibody precipitated both polypeptides of 140-150,000 and 46-50,000 dalton of 10S DNA polymerase alpha. The antibody also recognized the DNA polymerase alpha purified from human cells, but did pig DNA polymerase alpha only partially. The antibody did not crossreact with rat DNA polymerase alpha, calf DNA polymerase beta, virus DNA polymerase and E. coli DNA polymerase I. This antibody will be a useful tool for studying the mechanism of DNA replication in eukaryotic cells.

The proteins of hepatitis B Dane particle cores

Although several studies have been done to analyze the peptides of purified 22-nm HbsAg particles, no information has been published about the peptides of the core of the Dane particle which bears the other hepatitis B viral antigen. HbcAg. Dane particles and Dane particle cores (produced by NP-40 treatment of Dane particles) were purified by equilibrium centrifugation in CsCl density gradients. Two populations of Dane particles were observed at densities 1.27 and 1.24 g/ml, respectively. The higher buoyant density Dane particles yielded exclusively cores of buoyant density 1.38 g/ml in CsCl, and the lower buoyant density Dane particles yielded two kinds of cores with buoyant densities of 1.38 and 1.325 g/ml, respectively. Only the higher density Dane particles and cores manifested endogenously primed DNA polymerase activity. The peptides of density 1.38 g/ml Dane particle cores purified by equilibrium CsCl density gradient centrifugation and HBcAg particles from HBV infected chimpanzee liver purified in the same way were analyzed by SDS-polyacrylamide gel electrophoresis. Both kinds of particles were found to consistently contain 3 Coomassie blue staining peptides with approximate molecular weights of 19,000, 70,000 and 80,000 daltons (designated P-19, P-70 and P-80 respectively). In addition, the HBcAg particles from infected liver regularly yielded a protein component with molecular weight greater than 200,000 daltons. This component was occasionally present in electrophoresis runs of core peptides from only one of two patients. Its irregular appearance after gel electrophoresis suggests it may have been an aggregate not completely dissociated under the conditions used. The lower density core component consistently contained P-19, P-70, and P-80, and infrequently additional minor peptides of uncertain origin. The irregular occurrence of the minor peptides in varying amounts suggests they were not intrinsic core proteins.

Immunoaffinity purification of DNA polymerase delta

A monoclonal antibody against human DNA polymerase delta (pol delta) was isolated with properties suitable for its utilization for immunoaffinity chromatography. The antibody was immobilized after periodate oxidation and coupled to a hydrazide-activated support. Starting from a partially purified preparation, calf thymus pol delta was purified about 200-fold in a single step. Further purification on ssDNA-cellulose resulted in isolation of a homogeneous preparation. The amount of enzyme isolated, ca. 0.3 mg of pure pol delta from 0.75 kg of calf thymus, is about 15-fold greater than can be achieved by conventional procedures. This procedure provides a significant advance in the isolation of pol delta in allowing its facile isolation from tissues in good yield. The isolated enzyme consisted of two subunits of 125 and 50 kDa. Characterization of the enzyme showed that these two subunits remained associated on glycerol gradient ultracentrifugation even in the presence of 2.8 M urea.

Antibody to Epstein-Barr virus deoxyuridine triphosphate nucleotidohydrolase and deoxyribonucleotide polymerase in a chronic fatigue syndrome subset

BACKGROUND

A defined diagnostic panel differentiated patients who had been diagnosed with chronic fatigue syndrome (CFS), based upon Fukuda/Carruthers criteria. This diagnostic panel identified an Epstein-Barr virus (EBV) subset of patients (6), excluding for the first time other similar "clinical" conditions such as cytomegalovirus (CMV), human herpesvirus 6 (HHV6), babesiosis, ehrlichiosis, borreliosis, Mycoplasma pneumoniae, Chlamydia pneumoniae, and adult rheumatic fever, which may be mistakenly called CFS. CFS patients were treated with valacyclovir (14.3 mg/kg q6h) for ≥ 12 months. Each patient improved, based upon the Functional Activity Appraisal: Energy Index Score Healthcare Worker Assessment (EIPS), which is a validated (FSS-9), item scale with high degree of internal consistency measured by Cronbach's alpha.

METHODS

Antibody to EBV viral capsid antigen (VCA) IgM, EBV Diffuse Early Antigen EA(D), and neutralizing antibodies against EBV-encoded DNA polymerase and EBV-encoded dUTPase were assayed serially approximately every three months for 13-16 months from sera obtained from patients with CFS (6) and from sera obtained from twenty patients who had no history of CFS.

RESULTS

Antibodies to EBV EA(D) and neutralizing antibodies against the encoded-proteins EBV DNA polymerase and deoxyuridine triphosphate nucleotidohydrolase (dUTPase) were present in the EBV subset CFS patients. Of the sera samples obtained from patients with CFS 93.9% were positive for EA(D), while 31.6% of the control patients were positive for EBV EA(D). Serum samples were positive for neutralizing antibodies against the EBV-encoded dUTPase (23/52; 44.2%) and DNA polymerase (41/52; 78.8%) in EBV subset CFS patients, but negative in sera of controls.

CONCLUSIONS

There is prolonged elevated antibody level against the encoded proteins EBV dUTPase and EBV DNA polymerase in a subset of CFS patients, suggesting that this antibody panel could be used to identify these patients, if these preliminary findings are corroborated by studies with a larger number of EBV subset CFS patients.

Characterization of the POL3 gene product from Schizosaccharomyces pombe indicates inter-species conservation of the catalytic subunit of DNA polymerase delta

The Schizosaccharomyces pombe POL3 gene was isolated by sequence homology with a region of the Saccharomyces cerevisiae POL3 gene, the only gene sequenced to date encoding the catalytic subunit of eukaryotic DNA polymerase delta. The fission yeast POL3 gene contains a 52 base-pair (bp) intron and encodes a 3600 bp transcript the 5'-end of which is located 32 bp upstream from the initiation codon. The polypeptides predicted from budding and fission yeast POL3 genes share 52% of conserved amino acid residues and have a 60% identical central region. This structural conservation of the catalytic subunit of DNA polymerases delta is probably related to functional constraints. A portion of the most conserved region was used to raise antibodies against an S. pombe polymerase delta/beta-galactosidase fusion protein expressed in Escherichia coli. The purified antibodies recognized a 123,000 Da protein in S. pombe wild-type cell extracts and inhibited an aphidicolin-sensitive DNA polymerase activity that was distinct from DNA polymerase alpha. The antibodies also detected a 140,000 Da protein in extracts from different proliferating mammalian cells, indicating that the catalytic subunits of DNA polymerase delta are highly conserved between yeast and higher eukaryotes.

Cell cycle expression of two replicative DNA polymerases alpha and delta from Schizosaccharomyces pombe

We have investigated the expression of two Schizosaccharomyces pombe replicative DNA polymerases alpha and delta during the cell cycle. The pol alpha+ and pol delta+ genes encoding DNA polymerases alpha and delta were isolated from S. pombe. Both pol alpha+ and pol delta+ genes are single copy genes in haploid cells and are essential for cell viability. In contrast to Saccharomyces cerevisiae homologs, the steady-state transcripts of both S. pombe pol alpha+ and pol delta+ genes were present throughout the cell cycle. Sequence analysis of the pol alpha+ and pol delta+ genes did not reveal the Mlu I motifs in their upstream sequences that are involved in cell cycle-dependent transcription of S. cerevisiae DNA synthesis genes as well as the S. pombe cdc22+ gene at the G1/S boundary. However, five near-match Mlu I motifs were found in the upstream region of the pol alpha+ gene. S. pombe DNA polymerases alpha and delta proteins were also expressed constantly throughout the cell cycle. In addition, the enzymatic activity of the S. pombe DNA polymerase alpha measured by in vitro assay was detected at all stages of the cell cycle. Thus, these S. pombe replicative DNA polymerases, like that of S. pombe cdc17+ gene, are expressed throughout the cell cycle at the transcriptional and protein level. These results indicate that S. pombe has at least two regulatory modes for the expression of genes involved in DNA replication and DNA precursor synthesis.

Rad52 competes with Ku70/Ku86 for binding to S-region DSB ends to modulate antibody class-switch DNA recombination

Antibody class-switch DNA recombination (CSR) is initiated by AID-introduced DSBs in the switch (S) regions targeted for recombination, as effected by Ku70/Ku86-mediated NHEJ. Ku-deficient B cells, however, undergo (reduced) CSR through an alternative(A)-NHEJ pathway, which introduces microhomologies in S-S junctions. As microhomology-mediated end-joining requires annealing of single-strand DNA ends, we addressed the contribution of single-strand annealing factors HR Rad52 and translesion DNA polymerase θ to CSR. Compared with their Rad52+/+ counterparts, which display normal CSR, Rad52-/- B cells show increased CSR, fewer intra-Sμ region recombinations, no/minimal microhomologies in S-S junctions, decreased c-Myc/IgH translocations and increased Ku70/Ku86 recruitment to S-region DSB ends. Rad52 competes with Ku70/Ku86 for binding to S-region DSB ends. It also facilitates a Ku-independent DSB repair, which favours intra-S region recombination and mediates, particularly in Ku absence, inter-S-S recombination, as emphasized by the significantly greater CSR reduction in Rad52-/- versus Rad52+/+ B cells on Ku86 knockdown.

Enhanced delivery of exogenous peptides into the class I antigen processing and presentation pathway

Current immunization strategies, using peptide or protein antigens, generally fail to elicit cytotoxic-T-lymphocyte responses, since these antigens are unable to access intracellular compartments where loading of major histocompatibility complex class I (MHC-I) molecules occurs. In an attempt to circumvent this, we investigated whether the GM1 receptor-binding B subunit of Escherichia coli heat-labile toxin (EtxB) could be used to deliver class I epitopes. When a class I epitope was conjugated to EtxB, it was delivered into the MHC-I presentation pathway in a GM1-binding-dependent fashion and resulted in the appearance of MHC-I-epitope complexes at the cell surface. Importantly, we show that the efficiency of EtxB-mediated epitope delivery could be strikingly enhanced by incorporating, adjacent to the class I epitope, a 10-amino-acid segment from the C terminus of the DNA polymerase (Pol) of herpes simplex virus. The replacement of this 10-amino-acid segment by a heterologous sequence or the introduction of specific amino acid substitutions within this segment either abolished or markedly reduced the efficiency of class I epitope delivery. If the epitope was extended at its C terminus, EtxB-mediated delivery into the class I presentation pathway was found to be completely dependent on proteasome activity. Thus, by combining the GM1-targeting function of EtxB with the 10-amino-acid Pol segment, highly efficient delivery of exogenous epitopes into the endogenous pathway of class I antigen processing and presentation can be achieved.

Yeast DNA polymerases: antigenic relationship, use of RNA primer and associated exonuclease activity

Highly purified preparation of DNA polymerases A and B from yeast were compared with respect to antigenic relationship, ability to use ribonucleotide primers and associated nuclease activity. The following results were obtained. 1. Antiserum directed against DNA polymerase A inhibits this enzyme but does not interfere with activity of DNA polymerase B or of mitochondrial DNA polymerase, nor does it precipitate the latter two enzymes. 2. DNA polymerase A is capable of using oligo(ribouridylic acid) as a primer for the polymerization of dTMP. This reaction is not catalyzed by polymerase B to any significant extent. 3. Whereas DNA polymerase A is devoid of nuclease activity, DNA polymerase B catalyses an exonucleolytic release of mononucleotide units from the 3' end of polynucleotides. The results of several experiments suggest that this nuclease activity is associated with the DNA polymerase B molecule.

Evolutionary conservation of DNA polymerase beta structure

An immunological procedure that uses antiserum against homogeneous calf thymus DNA polymerase beta to detect immunoreactive peptides on NaDodSO4/polyacrylamide gel electrophoresis demonstrates a high degree of conservation of protein sequence and molecular weight for this enzyme, from parastic protozoans to man. By renaturation of DNA polymerase activity in situ after electrophoresis, the enzymatically active peptides are shown to correspond to the immunoreactive peptides. The persistence of sequence and molecular weight for the catalytic peptide of DNA polymerase beta through eons of evolutionary time suggests an essential role for this enzyme in DNA metabolism of complex cells.

Characterization of two monoclonal antibodies to Epstein-Barr virus diffuse early antigen which react to two different epitopes and have different biological function

Five monoclonal antibodies (mAbs) were identified using immunofluorescence that were specific for the Epstein-Barr virus (EBV) encoded 52/50 kDa early antigen (EA-D) protein complex. Evidence to suggest that these mAbs react with the same 52/50 kDa EA-D protein was obtained by Western blotting, immunoprecipitation and ELISA. Two of the mAbs, 90E2 and 214A9, neutralized EBV DNA polymerase activity. The 214A9 mAb also inhibited the activity of bacteriophage T4 DNA polymerase while the 90E2 mAb did not. These data suggest that the 90E2 and 214A9 mAbs recognize two different epitopes on the 52/50 kDa EA-D protein. The high frequency of recovery of hybridomas producing anti 52/50 kDa EA-D mAbs suggest that this protein may have an important role in EBV pathogenesis/replication.