Eukaryotic origin firing depends on assembly of the Cdc45-MCM-GINS (CMG) helicase. A key step is the recruitment of GINS that requires the leading-strand polymerase Pol epsilon, composed of Pol2, ...Dpb2, Dpb3, Dpb4. While a truncation of the catalytic N-terminal Pol2 supports cell division, Dpb2 and C-terminal Pol2 (C-Pol2) are essential for viability. Dpb2 and C-Pol2 are non-catalytic modules, shown or predicted to be related to an exonuclease and DNA polymerase, respectively. Here, we present the cryo-EM structure of the isolated C-Pol2/Dpb2 heterodimer, revealing that C-Pol2 contains a DNA polymerase fold. We also present the structure of CMG/C-Pol2/Dpb2 on a DNA fork, and find that polymerase binding changes both the helicase structure and fork-junction engagement. Inter-subunit contacts that keep the helicase-polymerase complex together explain several cellular phenotypes. At least some of these contacts are preserved during Pol epsilon-dependent CMG assembly on path to origin firing, as observed with DNA replication reconstituted in vitro.
The replisome unwinds and synthesizes DNA for genome duplication. In eukaryotes, the Cdc45–MCM–GINS (CMG) helicase and the leading-strand polymerase, Pol epsilon, form a stable assembly. The ...mechanism for coupling DNA unwinding with synthesis is starting to be elucidated, however the architecture and dynamics of the replication fork remain only partially understood, preventing a molecular understanding of chromosome replication. To address this issue, we conducted a systematic single-particle EM study on multiple permutations of the reconstituted CMG–Pol epsilon assembly. Pol epsilon contains two flexibly tethered lobes. The noncatalytic lobe is anchored to the motor of the helicase, whereas the polymerization domain extends toward the side of the helicase. We observe two alternate configurations of the DNA synthesis domain in the CMG-bound Pol epsilon. We propose that this conformational switch might control DNA template engagement and release, modulating replisome progression.
Eukaryotic cells initiate DNA replication from multiple origins, which must be tightly regulated to promote precise genome duplication in every cell cycle. To accomplish this, initiation is ...partitioned into two temporally discrete steps: a double hexameric minichromosome maintenance (MCM) complex is first loaded at replication origins during G1 phase, and then converted to the active CMG (Cdc45-MCM-GINS) helicase during S phase. Here we describe the reconstitution of budding yeast DNA replication initiation with 16 purified replication factors, made from 42 polypeptides. Origin-dependent initiation recapitulates regulation seen in vivo. Cyclin-dependent kinase (CDK) inhibits MCM loading by phosphorylating the origin recognition complex (ORC) and promotes CMG formation by phosphorylating Sld2 and Sld3. Dbf4-dependent kinase (DDK) promotes replication by phosphorylating MCM, and can act either before or after CDK. These experiments define the minimum complement of proteins, protein kinase substrates and co-factors required for regulated eukaryotic DNA replication.
Objective
SB5 is a biosimilar agent for adalimumab (ADA). The aim of this study was to evaluate the efficacy, pharmacokinetics (PK), safety, and immunogenicity of SB5 in comparison with reference ADA ...in patients with rheumatoid arthritis (RA).
Methods
In this phase III, randomized, double‐blind, parallel‐group study, patients with moderately to severely active RA despite treatment with methotrexate were randomized 1:1 to receive SB5 or reference ADA at a dosage of 40 mg subcutaneously every other week. The primary efficacy end point was the response rate based on the American College of Rheumatology 20% improvement criteria (ACR20) at week 24 in the per‐protocol set (completer analysis). Additional end points included efficacy, PK, safety, and immunogenicity assessments.
Results
Of the 544 patients randomized to receive a study drug, the full analysis set comprised 542 patients (269 in the SB5 group, 273 in the reference ADA group) and the per‐protocol set comprised 476 patients (239 receiving SB5, 237 receiving reference ADA). The ACR20 response rate at week 24 in the per‐protocol set was equivalent between those receiving SB5 and those receiving reference ADA (72.4% and 72.2%, respectively); the difference in the ACR20 response rate (0.1%, 95% confidence interval −7.83%, 8.13%) was within the predefined equivalence margin (±15%). Similar results were seen in the full analysis set (missing data being considered a nonresponse). The SB5 and reference ADA treatment groups were comparable across other end points, including the ACR 50% and ACR 70% improvement response rates, Disease Activity Score in 28 joints based on the erythrocyte sedimentation rate, PK data, incidence of treatment‐emergent adverse events, and the antidrug antibody response. Subgroup analyses showed that the efficacy and safety of SB5 and reference ADA were comparable regardless of antidrug antibody status.
Conclusion
The ACR20 response rate at week 24 was equivalent between patients treated with the biosimilar agent SB5 and those treated with reference ADA. SB5 and reference ADA were both well tolerated, with comparable safety profiles, in patients with RA.
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