Large T antigen on the simian virus 40 origin of replication: a 3D snapshot prior to DNA replication

Large T antigen is the replicative helicase of simian virus 40. Its specific binding to the origin of replication and oligomerization into a double hexamer distorts and unwinds dsDNA. In viral replication, T antigen acts as a functional homolog of the eukaryotic minichromosome maintenance factor MCM. T antigen is also an oncoprotein involved in transformation through interaction with p53 and pRb. We obtained the three-dimensional structure of the full-length T antigen double hexamer assembled at its origin of replication by cryoelectron microscopy and single-particle reconstruction techniques. The double hexamer shows different degrees of bending along the DNA axis. The two hexamers are differentiated entities rotated relative to each other. Isolated strands of density, putatively assigned to ssDNA, protrude from the hexamer–hexamer junction mainly at two opposite sites. The structure of the T antigen at the origin of replication can be understood as a snapshot of the dynamic events leading to DNA unwinding. Based on these results a model for the initiation of simian virus 40 DNA replication is proposed

Diagnosis of infection in hip and knee revision surgery: intraoperative frozen section analysis

In this study we validated intraoperatively the analysis of polymorphonuclear leucocyte frozen sections for diagnosis of infection in hip and knee revisions. Between 1996 and 2002 we examined sections and cultured periprosthetic tissues in prosthetic revision in 170 cases, including 146 cases (83 hips and 63 knees). We assessed sensitivity (SE), specificity (SP), positive predictive value (PPV), negative predictive value (NPV), Youden index, positive likelihood ratio (PLR) and negative likelihood ratio (NLR). We compared intraoperative findings and paraffin-embedded samples. The results in the knee group were SE=66.7%, SP=89.7% [95% confidence interval (CI)], PPV=81% (95% CI), NPV=81.4% (95% CI), Youden index=0.56, PLR=6.5 (95% CI) and NLR=0.4 (95% CI). In the paraffin-embedded samples the results were SE=91%, SP=87% (95% CI), PPV=81% (95% CI), NPV=94% (95% CI), PLR=7 (95% CI) and NLR=8.7 (95% CI). We found a significant difference. The results in the hip group were SE=50%, SP=100% (95% CI), PPV=100% (95% CI), NPV=94.9% (95% CI), Youden index=0.5 and PLR=0.5 (95% CI). In hip and knee prosthetic revision surgery the presence of polymorphonuclear cells correlates with infection, but their absence does not exclude it. It is a quick and inexpensive test that should be included in the diagnostic protocol in revision surgery. Level of evidence: diagnostic Study (investigating a diagnostic test), level I. See instructions to authors for a complete description of levels of evidence