Optimized incorporation of an unnatural fluorescent amino acid affords measurement of conformational dynamics governing high-fidelity DNA replication.

DNA polymerase from bacteriophage T7 undergoes large, substrate-induced conformational changes that are thought to account for high replication fidelity, but prior studies were adversely affected by mutations required to construct a Cys-lite variant needed for site-specific fluorescence labeling. Here we have optimized the direct incorporation of a fluorescent un-natural amino acid, (7-hydroxy-4-coumarin-yl)-ethylglycine, using orthogonal amber suppression machinery in Escherichia coli MS methods verify that the unnatural amino acid is only incorporated at one position with minimal background. We show that the single fluorophore provides a signal to detect nucleotide-induced conformational changes through equilibrium and stopped-flow kinetic measurements of correct nucleotide binding and incorporation. Pre-steady-state chemical quench methods show that the kinetics and fidelity of DNA replication catalyzed by the labeled enzyme are largely unaffected by the unnatural amino acid. These advances enable rigorous analysis to establish the kinetic and mechanistic basis for high-fidelity DNA replication.

Translesion synthesis DNA polymerases η, ι, and ν promote mutagenic replication through the anticancer nucleoside cytarabine.

Cytarabine (AraC) is the mainstay for the treatment of acute myeloid leukemia. Although complete remission is observed in a large proportion of patients, relapse occurs in almost all the cases. The chemotherapeutic action of AraC derives from its ability to inhibit DNA synthesis by the replicative polymerases (Pols); the replicative Pols can insert AraCTP at the 3' terminus of the nascent DNA strand, but they are blocked at extending synthesis from AraC. By extending synthesis from the 3'-terminal AraC and by replicating through AraC that becomes incorporated into DNA, translesion synthesis (TLS) DNA Pols could reduce the effectiveness of AraC in chemotherapy. Here we identify the TLS Pols required for replicating through the AraC templating residue and determine their error-proneness. We provide evidence that TLS makes a consequential contribution to the replication of AraC-damaged DNA; that TLS through AraC is conducted by three different pathways dependent upon Polη, Polι, and Polν, respectively; and that TLS by all these Pols incurs considerable mutagenesis. The prominent role of TLS in promoting proficient and mutagenic replication through AraC suggests that TLS inhibition in acute myeloid leukemia patients would increase the effectiveness of AraC chemotherapy; and by reducing mutation formation, TLS inhibition may dampen the emergence of drug-resistant tumors and thereby the high incidence of relapse in AraC-treated patients.

A PolH Transcript with a Short 3'UTR Enhances PolH Expression and Mediates Cisplatin Resistance.

Platinum-based anticancer drugs are widely used as a first-line drug for cancers, such as non-small cell lung carcinoma (NSCLC) and bladder cancer. However, the efficacy is limited due to intrinsic or acquired resistance to these drugs. DNA polymerase eta (PolH, Polη) belongs to the Y-family of DNA polymerases and mediates DNA translesion synthesis, a major mechanism for DNA damage tolerance. Here, we showed that a high level of PolH is associated with cisplatin resistance in lung and bladder cancer. Consistent with this, loss of PolH markedly attenuates cisplatin resistance in both cisplatin-sensitive and cisplatin-resistant lung cancer cells. Interestingly, we found that due to the presence of multiple polyadenylation sites, alternative polyadenylation (APA) produces three major PolH transcripts with various lengths of 3'untranslated region (3'UTR; 427-/2516-/6245-nt). We showed that the short PolH transcript with 427-nt 3'UTR is responsible for high expression of PolH in various cisplatin-resistant lung and bladder cancer cell lines. Importantly, loss of the short PolH transcript significantly sensitizes cancer cells to cisplatin treatment. Moreover, we found that miR-619 selectively inhibits the ability of the long PolH transcript with 6245-nt 3'UTR to produce PolH protein and, subsequently, PolH-dependent cell growth. Together, our data suggest that PolH expression is controlled by APA and that the short PolH transcript produced by APA can escape miR-619-mediated repression and, subsequently, confers PolH-mediated cisplatin resistance. SIGNIFICANCE: A short PolH transcript produced by alternative polyadenylation escapes repression by miR-619 and confers resistance to cisplatin.

Two Approaches to Enhance the Processivity and Salt Tolerance of Staphylococcus aureus DNA Polymerase.

In this article, two engineering-strategies were carried out to enhance the processivity of the DNA polymerase used in recombinase polymerase amplification (RPA). We demonstrate that covalent linkage of a non-specific, double-stranded DNA binding protein, Sso7d, to the large fragment of Staphylococcus aureus Pol I (Sau) caused a moderate enhancement of processivity and a significant improvement in the salt tolerance of Sau. Meanwhile, we provide evidence suggesting that insertion of the thioredoxin-binding domain from bacteriophage T7 DNA polymerase into the analogous position of the large fragment of Sau dramatically enhanced the processivity and mildly increased the salt tolerance of Sau when a host DNA binding protein, thioredoxin, was annexed. Both of these two strategies did not improve the amplifying performance of Sau in RPA, indicating that optimum processivity is crucial for amplifying efficiency.

Compartmentalized Self-Replication for Evolution of a DNA Polymerase.

Compartmentalized self-replication (CSR) is an emulsion PCR-based method for the selection of DNA polymerases. E. coli host cells expressing a library of DNA polymerases are emulsified so that no more than a single cell is present in a single emulsion droplet. In a subsequent emulsion PCR step, the DNA polymerase protein, as well as the plasmid encoding it are released into the emulsion droplet and the genes that created the most active or abundant polymerase variants are exponentially amplified and can be passed to the next round of CSR. CSR is a powerful method for engineering of polymerases since it allows selection under a variety of conditions, including the use of non-standard substrates. In this unit, we provide a step-by-step procedure for the selection of polymerases, using as an example the selection of reverse transcriptase activity starting from a library of Thermococcus kodakaraensis (KOD) DNA polymerase variants. © 2018 by John Wiley & Sons, Inc.

Efficient Translation of Epstein-Barr Virus (EBV) DNA Polymerase Contributes to the Enhanced Lytic Replication Phenotype of M81 EBV.

Epstein-Barr virus (EBV) is linked to the development of both lymphoid and epithelial malignancies worldwide. The M81 strain of EBV, isolated from a Chinese patient with nasopharyngeal carcinoma (NPC), demonstrates spontaneous lytic replication and high-titer virus production in comparison to the prototype B95-8 EBV strain. Genetic comparisons of M81 and B95-8 EBVs were previously been performed in order to determine if the hyperlytic property of M81 is associated with sequence differences in essential lytic genes. EBV SM is an RNA-binding protein expressed during early lytic replication that is essential for virus production. We compared the functions of M81 SM and B95-8 SM and demonstrate that polymorphisms in SM do not contribute to the lytic phenotype of M81 EBV. However, the expression level of the EBV DNA polymerase protein was much higher in M81- than in B95-8-infected cells. The relative deficiency in the expression of B95-8 DNA polymerase was related to the B95-8 genome deletion, which truncates the BALF5 3' untranslated region (UTR). Similarly, the insertion of bacmid DNA into the widely used recombinant B95-8 bacmid creates an inefficient BALF5 3' UTR. We further showed that the while SM is required for and facilitates the efficient expression of both M81 and B95-8 mRNAs regardless of the 3' UTR, the BALF5 3' UTR sequence is important for BALF5 protein translation. These data indicate that the enhanced lytic replication and virus production of M81 compared to those of B95-8 are partly due to the robust translation of EBV DNA polymerase required for viral DNA replication due to a more efficient BALF5 3' UTR in M81.IMPORTANCE Epstein-Barr virus (EBV) infects more than 90% of the human population, but the incidence of EBV-associated tumors varies greatly in different parts of the world. Thus, understanding the connection between genetic polymorphisms from patient isolates of EBV, gene expression phenotypes, and disease is important and may help in developing antiviral therapy. This study examines potential causes of the enhanced lytic replicative properties of M81 EBV isolated from a nasopharyngeal carcinoma (NPC) patient and provides new evidence for the role of the BALF5 gene 3' UTR sequence in DNA polymerase protein expression during lytic replication. Variation in the gene structure of the DNA polymerase gene may therefore contribute to lytic virus reactivation and pathogenesis.

Translesion Synthesis DNA Polymerase Kappa Is Indispensable for DNA Repair Synthesis in Cisplatin Exposed Dorsal Root Ganglion Neurons.

In the peripheral nervous system (PNS) in the absence of tight blood barrier, neurons are at increased risk of DNA damage, yet the question of how effectively PNS neurons manage DNA damage remains largely unanswered. Genotoxins in systemic circulation include chemotherapeutic drugs that reach peripheral neurons and damage their DNA. Because neurotoxicity of platinum-based class of chemotherapeutic drugs has been implicated in PNS neuropathies, we utilized an in vitro model of Dorsal Root Ganglia (DRGs) to investigate how peripheral neurons respond to cisplatin that forms intra- and interstrand crosslinks with their DNA. Our data revealed strong transcriptional upregulation of the translesion synthesis DNA polymerase kappa (Pol κ), while expression of other DNA polymerases remained unchanged. DNA Pol κ is involved in bypass synthesis of diverse DNA lesions and considered a vital player in cellular survival under injurious conditions. To assess the impact of Pol κ deficiency on cisplatin-exposed DRG neurons, Pol κ levels were reduced using siRNA. Pol κ targeting siRNA diminished the cisplatin-induced nuclear Pol κ immunoreactivity in DRG neurons and decreased the extent of cisplatin-induced DNA repair synthesis, as reflected in reduced incorporation of thymidine analog into nuclear DNA. Moreover, Pol κ depletion exacerbated global transcriptional suppression induced by cisplatin in DRG neurons. Collectively, these findings provide the first evidence for critical role of Pol κ in DNA damage response in the nervous system and call attention to implications of polymorphisms that modify Pol κ activity, on maintenance of genomic integrity and neuronal function in exogenously challenged PNS.

Persistent damaged bases in DNA allow mutagenic break repair in Escherichia coli.

Bacteria, yeast and human cancer cells possess mechanisms of mutagenesis upregulated by stress responses. Stress-inducible mutagenesis potentially accelerates adaptation, and may provide important models for mutagenesis that drives cancers, host pathogen interactions, antibiotic resistance and possibly much of evolution generally. In Escherichia coli repair of double-strand breaks (DSBs) becomes mutagenic, using low-fidelity DNA polymerases under the control of the SOS DNA-damage response and RpoS general stress response, which upregulate and allow the action of error-prone DNA polymerases IV (DinB), II and V to make mutations during repair. Pol IV is implied to compete with and replace high-fidelity DNA polymerases at the DSB-repair replisome, causing mutagenesis. We report that up-regulated Pol IV is not sufficient for mutagenic break repair (MBR); damaged bases in the DNA are also required, and that in starvation-stressed cells, these are caused by reactive-oxygen species (ROS). First, MBR is reduced by either ROS-scavenging agents or constitutive activation of oxidative-damage responses, both of which reduce cellular ROS levels. The ROS promote MBR other than by causing DSBs, saturating mismatch repair, oxidizing proteins, or inducing the SOS response or the general stress response. We find that ROS drive MBR through oxidized guanines (8-oxo-dG) in DNA, in that overproduction of a glycosylase that removes 8-oxo-dG from DNA prevents MBR. Further, other damaged DNA bases can substitute for 8-oxo-dG because ROS-scavenged cells resume MBR if either DNA pyrimidine dimers or alkylated bases are induced. We hypothesize that damaged bases in DNA pause the replisome and allow the critical switch from high fidelity to error-prone DNA polymerases in the DSB-repair replisome, thus allowing MBR. The data imply that in addition to the indirect stress-response controlled switch to MBR, a direct cis-acting switch to MBR occurs independently of DNA breakage, caused by ROS oxidation of DNA potentially regulated by ROS regulators.

Kinetics of Lagging-strand DNA Synthesis In Vitro by the Bacteriophage T7 Replication Proteins.

Here we provide protocols for the kinetic examination of lagging-strand DNA synthesis in vitro by the replication proteins of bacteriophage T7. The T7 replisome is one of the simplest replication systems known, composed of only four proteins, which is an attractive feature for biochemical experiments. Special emphasis is placed on the synthesis of ribonucleotide primers by the T7 primase-helicase, which are used by DNA polymerase to initiate DNA synthesis. Because the mechanisms of DNA replication are conserved across evolution, these protocols should be applicable, or useful as a conceptual springboard, to investigators using other model systems. The protocols described here are highly sensitive and an experienced investigator can perform these experiments and obtain data for analysis in about a day. The only specialized piece of equipment required is a rapid-quench flow instrument, but this piece of equipment is relatively common and available from various commercial sources. The major drawbacks of these assays, however, include the use of radioactivity and the relative low throughput.

Transcriptional Responses of the Bacterium Burkholderia terrae BS001 to the Fungal Host Lyophyllum sp. Strain Karsten under Soil-Mimicking Conditions.

In this study, the mycosphere isolate Burkholderia terrae BS001 was confronted with the soil fungus Lyophyllum sp. strain Karsten on soil extract agar plates in order to examine its transcriptional responses over time. At the initial stages of the experiment (T1-day 3; T2-day 5), contact between both partner organisms was absent, whereas in the final stage (T3-day 8), the two populations made intimate physical contact. Overall, a strong modulation of the strain BS001 gene expression patterns was found. First, the stationary-phase sigma factor RpoS, and numerous genes under its control, were strongly expressed as a response to the soil extract agar, and this extended over the whole temporal regime. In the system, B. terrae BS001 apparently perceived the presence of the fungal hyphae already at the early experimental stages (T1, T2), by strongly upregulating a suite of chemotaxis and flagellar motility genes. With respect to specific metabolism and energy generation, a picture of differential involvement in different metabolic routes was obtained. Initial (T1, T2) up- or downregulation of ethanolamine and mandelate uptake and utilization pathways was substituted by a strong investment, in the presence of the fungus, in the expression of putative metabolic gene clusters (T3). Specifically at T3, five clustered genes that are potentially involved in energy generation coupled to an oxidative stress response, and two genes encoding short-chain dehydrogenases/oxidoreductases (SDR), were highly upregulated. In contrast, the dnaE2 gene (related to general stress response; encoding error-prone DNA polymerase) was transcriptionally downregulated at this stage. This study revealed that B. terrae BS001, from a stress-induced state, resulting from the soil extract agar milieu, responds positively to fungal hyphae that encroach upon it, in a temporally dynamic manner. The response is characterized by phases in which the modulation of (1) chemotaxis, (2) metabolic activity, and (3) oxidative stress responses are key mechanisms.

Genomic Scars Generated by Polymerase Theta Reveal the Versatile Mechanism of Alternative End-Joining.

For more than half a century, genotoxic agents have been used to induce mutations in the genome of model organisms to establish genotype-phenotype relationships. While inaccurate replication across damaged bases can explain the formation of single nucleotide variants, it remained unknown how DNA damage induces more severe genomic alterations. Here, we demonstrate for two of the most widely used mutagens, i.e. ethyl methanesulfonate (EMS) and photo-activated trimethylpsoralen (UV/TMP), that deletion mutagenesis is the result of polymerase Theta (POLQ)-mediated end joining (TMEJ) of double strand breaks (DSBs). This discovery allowed us to survey many thousands of available C. elegans deletion alleles to address the biology of this alternative end-joining repair mechanism. Analysis of ~7,000 deletion breakpoints and their cognate junctions reveals a distinct order of events. We found that nascent strands blocked at sites of DNA damage can engage in one or more cycles of primer extension using a more downstream located break end as a template. Resolution is accomplished when 3' overhangs have matching ends. Our study provides a step-wise and versatile model for the in vivo mechanism of POLQ action, which explains the molecular nature of mutagen-induced deletion alleles.

[Downregulation of Human Adenovirus DNA Polymerase Gene by Modified siRNAs].

Human adenoviruses, in particular D8, D19, and D37, cause ocular infections. Currently, there is no available causally directed treatment, which efficiently counteracts adenoviral infectious diseases. In our previous work, we showed that gene silencing by means of RNA interference is an effective approach for downregulation of human species D adenoviruses replication. In this study, we compared the biological activity of siRNAs and their modified analogs targeting human species D adenoviruses DNA polymerase. We found that one of selectively 2'-O-methyl modified siRNAs mediates stable and long-lasting suppression of the target gene (12 days post transfection). We suppose that this siRNA can be used as a potential therapeutic agent against human species D adenoviruses.

REV3L, the catalytic subunit of DNA polymerase ζ, is involved in the progression and chemoresistance of esophageal squamous cell carcinoma.

Protein reversionless 3-like (REV3L), the catalytic subunit of DNA polymerase (pol) ζ, is well known to participate in error-prone translesion synthesis (TLS) with less stringent and lower processivity. Recent evidence has demonstrated that REV3L is involved in carcinogenesis and tumor progression. However, the function of REV3L remains unclear in esophageal squamous cell carcinoma (ESCC). In the present study, we examined REV3L expression in ESCC tissues and its association with clinicopathological parameters. REV3L was found to be significantly upregulated and correlated with lymph node metastasis and clinical stage in the ESCC tissues. To further investigate the potential role of REV3L in esophageal cancer, stable ESCC cell lines with suppression of REV3L expression were established. Downregulation of REV3L expression led to a decrease in cell proliferation and invasive capacity partly through suppression of cyclin D1 and survivin expression, and an increase in cellular sensitivity to 5-fluorouracil (5-FU) by induction of G1 phase arrest and apoptosis. Therefore, REV3L plays an important role in ESCC progression and chemoresistance, and is a potential diagnostic marker and therapeutic target for ESCC.

Synergistic effects by combination of ganciclovir and tricin on human cytomegalovirus replication in vitro.

It has been demonstrated as the first report that combination treatment with ganciclovir (GCV) and tricin (4',5,7-trihydroxy-3',5' -dimethoxyflavone), a derivative of Sasa albo-marginata, after human cytomegalovirus (HCMV) infection has synergistic effects on both infectious virus production and HCMV DNA synthesis in the human embryonic fibroblast cell line MRC-5. In this paper, we examined the anti-HCMV effects of GCV plus various concentrations of tricin, and tricin plus various concentrations of GCV in MRC-5 cells. We found that expression of the HCMV UL54 gene was significantly inhibited by combination of GCV with tricin when compared with GCV mono-treatment. These results suggest that tricin is a novel compound for combination therapy with GCV against HCMV replication. In addition, reduced-dose combination therapy may provide a direction for treatment in patients with HCMV infection while reducing drug toxicity.

Kynurenine Signaling Increases DNA Polymerase Kappa Expression and Promotes Genomic Instability in Glioblastoma Cells.

Overexpression of the translesion synthesis polymerase hpol κ in glioblastomas has been linked to poor patient prognosis; however, the mechanism promoting higher expression in these tumors remains unknown. We determined that activation of the aryl hydrocarbon receptor (AhR) pathway in glioblastoma cells leads to increased hpol κ mRNA and protein levels. We blocked nuclear translocation and DNA binding by AhR in glioblastoma cells using a small-molecule and observed decreased hpol κ expression. Pharmacological inhibition of tryptophan-2,3-dioxygenase (TDO), the enzyme largely responsible for activating AhR in glioblastoma, led to a decrease in the endogenous AhR agonist kynurenine and a corresponding decrease in hpol κ protein levels. Importantly, we discovered that inhibiting TDO activity, AhR signaling, or suppressing hpol κ expression with RNA interference led to decreased chromosomal damage in glioblastoma cells. Epistasis assays further supported the idea that TDO activity, activation of AhR signaling, and the resulting overexpression of hpol κ function primarily in the same pathway to increase endogenous DNA damage. These findings indicate that upregulation of hpol κ through glioblastoma-specific TDO activity and activation of AhR signaling likely contributes to the high levels of replication stress and genomic instability observed in these tumors.

REV3L modulates cisplatin sensitivity of non-small cell lung cancer H1299 cells.

Lung cancer remains the leading cause of cancer-related mortality worldwide and non-small cell lung cancer (NSCLC) accounts for approximately 80-85% of all cases of lung cancer. Cisplatin plays a significant role in the management of human lung cancer. Translesion DNA synthesis (TLS) is involved in DNA damage repair. DNA polymerase Î¶ (Pol Î¶) is able to mediate the DNA replication bypass of DNA damage, which is suggested to be involved in chemoresistance. REV3L is the catalytic subunit of Pol Î¶. Due to its critical role in translesion DNA synthesis, whether REV3L modulates cisplatin response in NSCLC cells remains unknown. In this study, REV3L overexpression and silencing H1299 cell lines were established. The reports showed that cisplatin induced the expression of REV3L by recruiting Sp1 to its promoter. Similar results were obtained when the ability of the cells to express luciferase from a platinated plasmid was measured. Co-transfection of the reporter with the REV3L overexpression vector or REV3L plus REV7L significantly enhanced the reporter activity. Nuclear condensation and fragmentation of shRNA-REV3L H1299 cells were more pronounced than shRNA-NC H1299 cells after cisplatin exposure, indicating that REV3L overexpression abolished cisplatin-induced DNA damage. Moreover, a forced expression of REV3L conferred the resistance of H1299 cells to cisplatin, whereas the knockdown of REV3L sensitized cisplatin efficacy in H1299 cells. Taken together, we demonstrated that inhibition of REV3L sensitized lung cancer H1299 cells to cisplatin treatment. Thus, REV3L may be a novel target for the chemotherapy of NSCLC.

Expression and Characterization of the RKOD DNA Polymerase in Pichia pastoris.

The present study assessed high-level expression of the KOD DNA polymerase in Pichia pastoris. Thermococcus kodakaraensis KOD1 is a DNA polymerase that is widely used in PCR. The DNA coding sequence of KOD was optimized based on the codon usage bias of P. pastoris and synthesized by overlapping PCR, and the nonspecific DNA-binding protein Sso7d from the crenarchaeon Sulfolobus solfataricus was fused to the C-terminus of KOD. The resulting novel gene was cloned into a pHBM905A vector and introduced into P. pastoris GS115 for secretory expression. The yield of the target protein reached approximately 250 mg/l after a 6-d induction with 1% (v/v) methanol in shake flasks. This yield is much higher than those of other DNA polymerases expressed heterologously in Escherichia coli. The recombinant enzyme was purified, and its enzymatic features were studied. Its specific activity was 19,384 U/mg. The recombinant KOD expressed in P. pastoris exhibited excellent thermostability, extension rate and fidelity. Thus, this report provides a simple, efficient and economic approach to realize the production of a high-performance thermostable DNA polymerase on a large scale. This is the first report of the expression in yeast of a DNA polymerase for use in PCR.

DNA polymerase ζ-dependent lesion bypass in Saccharomyces cerevisiae is accompanied by error-prone copying of long stretches of adjacent DNA.

Translesion synthesis (TLS) helps cells to accomplish chromosomal replication in the presence of unrepaired DNA lesions. In eukaryotes, the bypass of most lesions involves a nucleotide insertion opposite the lesion by either a replicative or a specialized DNA polymerase, followed by extension of the resulting distorted primer terminus by DNA polymerase ζ (Polζ). The subsequent events leading to disengagement of the error-prone Polζ from the primer terminus and its replacement with an accurate replicative DNA polymerase remain largely unknown. As a first step toward understanding these events, we aimed to determine the length of DNA stretches synthesized in an error-prone manner during the Polζ-dependent lesion bypass. We developed new in vivo assays to identify the products of mutagenic TLS through a plasmid-borne tetrahydrofuran lesion and a UV-induced chromosomal lesion. We then surveyed the region downstream of the lesion site (in respect to the direction of TLS) for the presence of mutations indicative of an error-prone polymerase activity. The bypass of both lesions was associated with an approximately 300,000-fold increase in the mutation rate in the adjacent DNA segment, in comparison to the mutation rate during normal replication. The hypermutated tract extended 200 bp from the lesion in the plasmid-based assay and as far as 1 kb from the lesion in the chromosome-based assay. The mutation rate in this region was similar to the rate of errors produced by purified Polζ during copying of undamaged DNA in vitro. Further, no mutations downstream of the lesion were observed in rare TLS products recovered from Polζ-deficient cells. This led us to conclude that error-prone Polζ synthesis continues for several hundred nucleotides after the lesion bypass is completed. These results provide insight into the late steps of TLS and show that error-prone TLS tracts span a substantially larger region than previously appreciated.

REV3L, a promising target in regulating the chemosensitivity of cervical cancer cells.

REV3L, the catalytic subunit of DNA Polymerase ζ (Polζ), plays a significant role in the DNA damage tolerance mechanism of translesion synthesis (TLS). The role of REV3L in chemosensitivity of cervical cancer needs exploration. In the present study, we evaluated the expression of the Polζ protein in paraffin-embedded tissues using immunohistochemistry and found that the expression of Polζ in cervical cancer tissues was higher than that in normal tissues. We then established some cervical cancer cell lines with REV3L suppression or overexpression. Depletion of REV3L suppresses cell proliferation and colony formation of cervical cancer cells through G1 arrest, and REV3L promotes cell proliferation and colony formation of cervical cancer cells by promoting G1 phase to S phase transition. The suppression of REV3L expression enhanced the sensitivity of cervical cancer cells to cisplatin, and the overexpression of REV3L conferred resistance to cisplatin as evidenced by the alteration of apoptosis rates, and significantly expression level changes of anti-apoptotic proteins B-cell lymphoma 2 (Bcl-2), myeloid cell leukemia sequence 1 (Mcl-1) and B-cell lymphoma-extra large (Bcl-xl) and proapoptotic Bcl-2-associated x protein (Bax). Our data suggest that REV3L plays an important role in regulating cervical cancer cellular response to cisplatin, and thus targeting REV3L may be a promising way to alter chemosensitivity in cervical cancer patients.

Development of an efficient process intensification strategy for enhancing Pfu DNA polymerase production in recombinant Escherichia coli.

An efficient induction strategy that consisted of multiple additions of small doses of isopropyl-ß-D-thiogalactopyranoside (IPTG) in the early cell growth phase was developed for enhancing Pfu DNA polymerase production in Escherichia coli. In comparison to the most commonly used method of a single induction of 1 mM IPTG, the promising induction strategy resulted in an increase in the Pfu activity of 13.5% in shake flasks, while simultaneously decreasing the dose of IPTG by nearly half. An analysis of the intracellular IPTG concentrations indicated that the cells need to maintain an optimum intracellular IPTG concentration after 6 h for efficient Pfu DNA polymerase production. A significant increase in the Pfu DNA polymerase activity of 31.5% under the controlled dissolved oxygen concentration of 30% in a 5 L fermentor was achieved using the multiple IPTG induction strategy in comparison with the single IPTG induction. The induction strategy using multiple inputs of IPTG also avoided over accumulation of IPTG and reduced the cost of Pfu DNA polymerase production.