Recent cryo-EM structures of human DNA polymerase ε (Pol ε) bound to PCNA position a Pol ε-specific thumb insertion (polymerase thumb insertion; PTI) adjacent to a PCNA protomer, suggesting a regulatory role in DNA synthesis. To define the functional contribution of this region, we generated alanine-substitution variants in the yeast Pol ε thumb domain, targeting the PTI (SLED1131-1134→AAAA; polε-SLED) and an adjacent conserved loop (PVTE1101-1104→AAAA; polε-PVTE and KPFN1096-1099→AAAA; polε-KPFN). polε-SLED displayed increased intrinsic processivity, efficient bypass of DNA secondary structures, and enhanced synthesis on long templates, consistent with reduced pausing. In contrast, a previous study extended this substitution to six amino acids, SLEDLD1131-1136→AAAAAA, and found a reversed effect, a reduced processivity, indicating that subtle perturbations in this insertion can have opposing functional consequences. polε-PVTE shifted polymerase activity toward exonuclease proofreading and was not fully rescued by PCNA on long templates, whereas polε-KPFN retained near-wild-type activity but showed increased sensitivity to secondary structures that was alleviated by PCNA. In vivo, the corresponding pol2-SLED allele caused a modest mutator phenotype, while pol2-PVTE and pol2-KPFN showed little or no increase. Together, these results indicate that the PTI fine-tunes intrinsic processivity and proofreading to maintain replication fidelity during leading-strand synthesis.

Disruptions in deoxynucleoside triphosphate (dNTP) supply impair DNA replication and lead to genomic instability. While exogenous ribonucleosides (rNuc) have been suggested to alleviate replication stress by increasing dNTP levels, their precise metabolic effects remain unclear. Here, we show that rNuc supplementation primarily elevates CTP and UTP levels, with only modest increases in dCTP, and has minimal impact on replication fork speed across multiple mammalian cell lines. In contrast, thymidine (dThd), either alone or in combination with rNuc-as in EmbryoMax Nucleosides-significantly increases dTTP and dGTP levels, leading to accelerated replication fork progression. Notably, dThd, rather than rNuc, drives fork acceleration and counteracts fork slowdown caused by elevated dUTP, consistent with primer extension assays showing that dUTP transiently inhibits Pol ϵ-mediated DNA synthesis at template adenines. These results clarify the distinct roles of nucleosides in nucleotide metabolism, providing a mechanistic basis for how dThd promotes fork progression and preserves genomic stability.

DNA replication relies on precise coordination between proteins, including the sliding clamp proliferating cell nuclear antigen (PCNA), which encircles DNA to interact with key players in replication and repair. While biochemical studies have demonstrated interactions between PCNA and DNA polymerases δ and ε during DNA synthesis, the functional role of the Pol ε–PCNA interaction in vivo, particularly during leading strand synthesis, remains to be elucidated. To address this question, we employed AlphaFold to model how PCNA interact with four-subunit yeast Pol ε. Our models revealed two distinct points of interaction between Pol ε and PCNA: one at the P-domain and another at a PIP-box, a classical PCNA interaction motif. To validate these findings, we generated mutants that disrupted the Pol ε–PCNA interaction interface. Biochemical assays demonstrated that the PIP-box is critical for this interaction, with the P-domain serving as a secondary contact point. Notably, introducing these mutants into yeast, caused no phenotype in a wild-type background. However, when fewer origins are firing, resulting in longer stretches of leading strand synthesis before forks converge, strains expressing a Pol ε mutant lacking interaction with PCNA showed slower growth. These findings suggest that PCNA enhances the processivity of Pol ε both in vitro and in vivo.

The stability of cellular phenotypes in developing organisms depends on error-free transmission of epigenetic and genetic information during mitosis. Methylation of cytosine residues in genomic DNA is a key epigenetic mark that modulates gene expression and prevents genome instability. Here, we report on a genetic test of the relationship between DNA replication and methylation in the context of the developing vertebrate organism instead of cell lines. Our analysis is based on the identification of hypomorphic alleles of dnmt1 , encoding the DNA maintenance methylase Dnmt1, and pole1 , encoding the catalytic subunit of leading-strand DNA polymerase epsilon holoenzyme (Pole). Homozygous dnmt1 mutants exhibit genome-wide DNA hypomethylation, whereas the pole1 mutation is associated with increased DNA methylation levels. In dnmt1 / pole1 double-mutant zebrafish larvae, DNA methylation levels are restored to near normal values, associated with partial rescue of mutant-associated transcriptional changes and phenotypes. Hence, a balancing antagonism between DNA replication and maintenance methylation buffers against replicative errors contributing to the robustness of vertebrate development.

Two recent studies provide structural insights into how human DNA polymerase epsilon (Pol epsilon) interacts with PCNA to form a processive holoenzyme on the leading strand. A series of cryo-EM images offer structural information on the proofreading process, showing how DNA is transferred between the polymerase and exonuclease sites in human Pol epsilon.

In the evolving landscape of sustainable biopharmaceutical process development, the utilization of bacteria in the production of various compounds via fermentation has attracted extensive attention from scientists. A successful fermentation process and the release of its associated products hinge on the synergy between an efficient bacterial strain and the formulation of a suitable growth medium. Balancing all nutrient levels of a growth medium to maximize microbial growth and the product quality is quite an intricate task. In this context, significant advancements have been achieved via the strategic implementation of design-of-experiment (DOE) methodologies and the utilization of parallel microbioreactor systems. This work presents a case study of the fermentation growth medium optimization of a Gram-negative bacterium of the Neisseriaceae family that releases outer membrane vesicles (OMVs), which represent a potential vaccine platform. To achieve this, the ability of Sartorius MODDE®13 DOE software to explore multiple variables and their interactions was combined with the functionality of a Sartorius Ambr® 15F parallel microbioreactor system. The findings reported in this study have led to the design of a well-suited fermentation medium for a Gram-negative bacterium and an improvement in the quality of the OMVs produced from it.

Raman spectroscopy is widely used in monitoring and controlling cell cultivations for biopharmaceutical drug manufacturing. However, its implementation for culture monitoring in the cell line development stage has received little attention. Therefore, the impact of clonal differences, such as productivity and growth, on the prediction accuracy and transferability of Raman calibration models is not yet well described. Raman OPLS models were developed for predicting titer, glucose and lactate using eleven CHO clones from a single cell line. These clones exhibited diverse productivity and growth rates. The calibration models were evaluated for clone-related biases using clone-wise linear regression analysis on cross validated predictions. The results revealed that clonal differences did not affect the prediction of glucose and lactate, but titer models showed a significant clone-related bias, which remained even after applying variable selection methods. The bias was associated with clonal productivity and lead to increased prediction errors when titer models were transferred to cultivations with productivity levels outside the range of their training data. The findings demonstrate the feasibility of Raman-based monitoring of glucose and lactate in cell line development with high accuracy. However, accurate titer prediction requires careful consideration of clonal characteristics during model development.

The cellular imbalance between high concentrations of ribonucleotides (NTPs) and low concentrations of deoxyribonucleotides (dNTPs), is challenging for DNA polymerases when building DNA from dNTPs. It is currently believed that DNA polymerases discriminate against NTPs through a steric gate model involving a clash between a tyrosine and the 2'-hydroxyl of the ribonucleotide in the polymerase active site in B-family DNA polymerases. With the help of crystal structures of a B-family polymerase with a UTP or CTP in the active site, molecular dynamics simulations, biochemical assays and yeast genetics, we have identified a mechanism by which the finger domain of the polymerase sense NTPs in the polymerase active site. In contrast to the previously proposed polar filter, our experiments suggest that the amino acid residue in the finger domain senses ribonucleotides by steric hindrance. Furthermore, our results demonstrate that the steric gate in the palm domain and the sensor in the finger domain are both important when discriminating NTPs. Structural comparisons reveal that the sensor residue is conserved among B-family polymerases and we hypothesize that a sensor in the finger domain should be considered in all types of DNA polymerases.

Background: Lung cancer can be detected by measuring the patient’s plasma metabolomic profile using nuclear magnetic resonance (NMR) spectroscopy. This NMR-based plasma metabolomic profile is patient-specific and represents a snapshot of the patient’s metabolite concentrations. The onset of non-small cell lung cancer (NSCLC) causes a change in the metabolite profile. However, the level of metabolic changes after complete NSCLC removal is currently unknown. Patients and methods: Fasted pre- and postoperative plasma samples of 74 patients diagnosed with resectable stage I-IIIA NSCLC were analyzed using 1H-NMR spectroscopy. NMR spectra (s = 222) representing two preoperative and one postoperative plasma metabolite profile at three months after surgical resection were obtained for all patients. In total, 228 predictors, i.e., 228 variables representing plasma metabolite concentrations, were extracted from each NMR spectrum. Two types of supervised multivariate discriminant analyses were used to train classifiers presenting a strong differentiation between the pre- and postoperative plasma metabolite profiles. The validation of these trained classification models was obtained by using an independent dataset. Results: A trained multivariate discriminant classification model shows a strong differentiation between the pre- and postoperative NSCLC profiles with a specificity of 96% (95% CI [86–100]) and a sensitivity of 92% (95% CI [81–98]). Validation of this model results in an excellent predictive accuracy of 90% (95% CI [77–97]) and an AUC value of 0.97 (95% CI [0.93–1]). The validation of a second trained model using an additional preoperative control sample dataset confirms the separation of the pre- and postoperative profiles with a predictive accuracy of 93% (95% CI [82–99]) and an AUC value of 0.97 (95% CI [0.93–1]). Metabolite analysis reveals significantly increased lactate, cysteine, asparagine and decreased acetate levels in the postoperative plasma metabolite profile. Conclusions: The results of this paper demonstrate that surgical removal of NSCLC generates a detectable metabolic shift in blood plasma. The observed metabolic shift indicates that the NSCLC metabolite profile is determined by the tumor’s presence rather than donor-specific features. Furthermore, the ability to detect the metabolic difference before and after surgical tumor resection strongly supports the prospect that NMR-generated metabolite profiles via blood samples advance towards early detection of NSCLC recurrence.

BACKGROUND:Monoclonal antibodies (mAbs) are leading types of 'blockbuster' biotherapeutics worldwide; they have been successfully used to treat various cancers and chronic inflammatory and autoimmune diseases. Biotherapeutics process development and manufacturing are complicated due to lack of understanding the factors that impact cell productivity and product quality attributes. Understanding complex interactions between cells, media, and process parameters on the molecular level is essential to bring biomanufacturing to the next level. This can be achieved by analyzing cell culture metabolic levels connected to vital process parameters like viable cell density (VCD). However, VCD and metabolic profiles are dynamic parameters and inherently correlated with time, leading to a significant correlation without actual causality. Many time-series methods deal with such issues. However, with metabolic profiling, the number of measured variables vastly exceeds the number of experiments, making most of existing methods ill-suited and hard to interpret.METHODS AND MAJOR RESULTS:Here we propose an alternative workflow using hierarchical dimension reduction to visualize and interpret the relation between evolution of metabolic profiles and dynamic process parameters. The first step of proposed method is focused on finding predictive relation between metabolic profiles and process parameter at all time points using OPLS regression. For each time point, the p(corr) obtained from OPLS model is considered as a differential metabogram and is further assessed using principal components analysis (PCA).CONCLUSIONS:Compared to traditional batch modeling, applying proposed methodology on metabolic data from Chinese Hamster Ovary (CHO) antibody production characterized the dynamic relation between metabolic profiles and critical process parameters.

Abstract Amino acid substitutions in the exonuclease domain of DNA polymerase ϵ (Polϵ) cause ultramutated tumors. Studies in model organisms suggested pathogenic mechanisms distinct from a simple loss of exonuclease. These mechanisms remain unclear for most recurrent Polϵ mutations. Particularly, the highly prevalent V411L variant remained a long-standing puzzle with no detectable mutator effect in yeast despite the unequivocal association with ultramutation in cancers. Using purified four-subunit yeast Polϵ, we assessed the consequences of substitutions mimicking human V411L, S459F, F367S, L424V and D275V. While the effects on exonuclease activity vary widely, all common cancer-associated variants have increased DNA polymerase activity. Notably, the analog of Polϵ-V411L is among the strongest polymerases, and structural analysis suggests defective polymerase-to-exonuclease site switching. We further show that the V411L analog produces a robust mutator phenotype in strains that lack mismatch repair, indicating a high rate of replication errors. Lastly, unlike wild-type and exonuclease-dead Polϵ, hyperactive variants efficiently synthesize DNA at low dNTP concentrations. We propose that this characteristic could promote cancer cell survival and preferential participation of mutator polymerases in replication during metabolic stress. Our results support the notion that polymerase fitness, rather than low fidelity alone, is an important determinant of variant pathogenicity.

The in vitro reconstitution of origin firing was a key step toward the biochemical reconstitution of eukaryotic DNA replication in budding yeast. Today the basic replication assay involves proteins purified from 24 separate protocols that have evolved since their first publication, and as a result, the efficiency and reliability of the in vitro replication system has improved. Here we will present protocols for all 24 purifications together with a general protocol for the in vitro replication assay and some tips for troubleshooting problems with the assay.

Many DNA replication and DNA repair enzymes have been found to carry [4Fe4S] clusters. The major leading strand polymerase, DNA polymerase ε (Pol ε) from Saccharomyces cerevisiae, was recently reported to have a [4Fe4S] cluster located within the catalytic domain of the largest subunit, Pol2. Here the redox characteristics of the [4Fe4S] cluster in the context of that domain, Pol2CORE, are explored using DNA electrochemistry, and the effects of oxidation and rereduction on polymerase activity are examined. The exonuclease deficient variant D290A/E292A, Pol2COREexo-, was used to limit DNA degradation. While no redox signal is apparent for Pol2COREexo- on DNA-modified electrodes, a large cathodic signal centered at -140 mV vs NHE is observed after bulk oxidation. A double cysteine to serine mutant (C665S/C668S) of Pol2COREexo-, which lacks the [4Fe4S] cluster, shows no similar redox signal upon oxidation. Significantly, protein oxidation yields a sharp decrease in polymerization, while rereduction restores activity almost to the level of untreated enzyme. Moreover, the addition of reduced EndoIII, a bacterial DNA repair enzyme containing [4Fe4S]2+, to oxidized Pol2COREexo- bound to its DNA substrate also significantly restores polymerase activity. In contrast, parallel experiments with EndoIIIY82A, a variant of EndoIII, defective in DNA charge transport (CT), does not show restoration of activity of Pol2COREexo-. We propose a model in which EndoIII bound to the DNA duplex may shuttle electrons through DNA to the DNA-bound oxidized Pol2COREexo- via DNA CT and that this DNA CT signaling offers a means to modulate the redox state and replication by Pol ε.

Single-stranded DNA breaks, or nicks, are amongst the most common forms of DNA damage in cells. They can be repaired by ligation; however, if a nick occurs just ahead of an approaching replisome, the outcome is a collapsed replication fork comprising a single-ended double-strand break and a 'hybrid nick' with parental DNA on one side and nascent DNA on the other (Figure 1A). We realized that in eukaryotic cells, where replication initiates from multiple replication origins, a fork from an adjacent origin can promote localized re-replication if the hybrid nick is ligated. We have modelled this situation with purified proteins in vitro and have found that there is, indeed, an additional hazard that eukaryotic replisomes face. We discuss how this problem might be mitigated.

Single-stranded DNA breaks, including simple nicks, are amongst the most common forms of DNA damage in cells. They can be readily repaired by ligation; however, if a nick occurs just ahead of an approaching replisome, the outcome is a ‘collapsed’ replication fork in which the nick is converted into a single-ended double-strand DNA break. Attention has largely focused on the processes by which this broken end is used to prime replication restart. We realized that in eukaryotic cells, where replication initiates from multiple replication origins, a second fork converging on the collapsed fork offers additional opportunities for repair, but also generates a substrate that can promote localized re-replication. We have modelled this with purified proteins in vitro and have found that there is, indeed, an additional hazard that eukaryotic replisomes face. We discuss how this problem might be mitigated.

The number of national reference populations that are whole-genome sequenced are rapidly increasing. Partly driving this development is the fact that genetic disease studies benefit from knowing the genetic variation typical for the geographical area of interest. A whole-genome sequenced Swedish national reference population (n=1000) has been recently published but with few samples from northern Sweden. In the present study we have whole-genome sequenced a control population (n=300) (ACpop) from Västerbotten County, a sparsely populated region in northern Sweden previously shown to be genetically different from southern Sweden. The aggregated variant frequencies within ACpop are publicly available (DOI 10.17044/NBIS/G000005) to function as a basic resource in clinical genetics and for genetic studies. Our analysis of ACpop, representing approximately 0.11% of the population in Västerbotten, indicates the presence of a genetic substructure within the county. Furthermore, a demographic analysis showed that the population from which samples were drawn was to a large extent geographically stationary, a finding that was corroborated in the genetic analysis down to the level of municipalities. Including ACpop in the reference population when imputing unknown variants in a Västerbotten cohort resulted in a strong increase in the number of high-confidence imputed variants (up to 81% for variants with minor allele frequency < 5%). ACpop was initially designed for cancer disease studies, but the genetic structure within the cohort will be of general interest for all genetic disease studies in northern Sweden.

In eukaryotes, the duplication of the genome requires three different DNA polymerases with separate functions. Both genetic experiments and biochemical experiments have shown that DNA Polymerase epsilon is responsible for the bulk synthesis of the leading strand during DNA replication. In addition, it was recently shown that a mutation in the exonuclease domain of Pol epsilon, leads to an impaired proofreading capacity and is responsible for a very high mutation load in sporadic tumors. We have in addition to biochemical and genetic experiments solved a series of ternary structures of the catalytic core of Pol2 (142 kDa), the catalytic subunit of yeast Pol epsilon. I will here discuss some of our most recent findings, for example the structural basis for the very high processivity of DNA polymerase epsilon, the presence of an Fe-S cluster in the catalytic domain, and how a single amino acid substitution (P301R in yeast, orthologous to P286R in human Pol epsilon) can alter the high-fidelity polymerase to become a very strong mutator polymerase. The structure, in combination with molecular dynamics simulations, revealed major differences between Pol epsilon P301R and the catalytically inactive Pol epsilon D290A,E292A in the mechanism of exonuclease inactivation, and help explain the vastly stronger mutagenic and tumorigenic effects of the cancer variant.

Whole-genome sequencing is a promising approach for human autosomal dominant disease studies. However, the vast number of genetic variants observed by this method constitutes a challenge when trying to identify the causal variants. This is often handled by restricting disease studies to the most damaging variants, e.g. those found in coding regions, and overlooking the remaining genetic variation. Such a biased approach explains in part why the genetic causes of many families with dominantly inherited diseases, in spite of being included in whole-genome sequencing studies, are left unsolved today. Here we explore the use of a geographically matched control population to minimize the number of candidate disease-causing variants without excluding variants based on assumptions on genomic position or functional predictions. To exemplify the benefit of the geographically matched control population we apply a typical disease variant filtering strategy in a family with an autosomal dominant form of colorectal cancer. With the use of the geographically matched control population we end up with 26 candidate variants genome wide. This is in contrast to the tens of thousands of candidates left when only making use of available public variant datasets. The effect of the local control population is dual, it (1) reduces the total number of candidate variants shared between affected individuals, and more importantly (2) increases the rate by which the number of candidate variants are reduced as additional affected family members are included in the filtering strategy. We demonstrate that the application of a geographically matched control population effectively limits the number of candidate disease-causing variants and may provide the means by which variants suitable for functional studies are identified genome wide.

DNA polymerase epsilon (Pol epsilon), the major leading-strand DNA polymerase in eukaryotes, has a catalytic subunit (Pol2) and three non-catalytic subunits. The N-terminal half of Pol2 (Pol2(CORE)) exhibits both polymerase and exonuclease activity. It has been suggested that both the non-catalytic C-terminal domain of Pol2 (with the two cysteine motifs CysA and CysB) and Pol2(CORE) (with the CysX cysteine motif) are likely to coordinate an Fe-S cluster. Here, we present two new crystal structures of Pol2(CORE) with an Fe-S cluster bound to the CysX motif, supported by an anomalous signal at that position. Furthermore we show that purified four-subunit Pol epsilon, Pol epsilon CysA(MUT) (C2111S/C2133S), and Pol epsilon CysB(MUT) (C2167S/C2181S) all have an Fe-S cluster that is not present in Pol epsilon CysX(MUT) (C665S/C668S). Pol epsilon CysA(MUT) and Pol epsilon CysB(MUT) behave similarly to wildtype Pol epsilon in in vitro assays, but Pol epsilon CysX(MUT) has severely compromised DNA polymerase activity that is not the result of an excessive exonuclease activity. Tetrad analyses show that haploid yeast strains carrying CysX(MUT) are inviable. In conclusion, Pol epsilon has a single Fe-S cluster bound at the base of the P-domain, and this Fe-S cluster is essential for cell viability and polymerase activity.