[en] AESJ Nuclear Safety Division held 'Fukushima Dai-ichi Accident Seminar' eight times from February 17 to December 19, 2012 for the analysis and evaluation of meltdown accident occurred at Fukushima Dai-ichi Nuclear Power Station caused by 'The 2011 off the Pacific coast of Tohoku Earthquake'. 'Report on the Fukushima Dai-ichi Accident Seminar - what was wrong and what should been down in future -' was issued in March 2013 based on summary report and discussion results for each seminar, which would be published as five special articles of the AESJ journal. This report (first article) was outline of the Report and described objective and history of seminar, digest of incidents occurred at Fukushima Dai-ichi and other nuclear power stations affected by earthquakes and tsunamis, and main conclusions of seminar. Lessons learned from the accident and proposals were on the following items: (1) safety assurance by defense-in-depth principle, (2) severe accident measures (accident management) and assurance of their effectiveness, (3) nuclear emergency preparedness, (4) safety research in future, (5) nuclear safety regulations, (6) risk communications essential to safety and common to various aspects and phases, and (7) obligations of Nuclear Safety Division and academia. (T. Tanaka)

[en] The dose rates from the turbine building of the boiling water reactor were measured with the NaI scintillation counter. The measurements were compared with the result of the calculation by the Monte-Carlo N-Particle Transport Code System (MCNP) which is a radiation analysis calculation code. Measurements and the calculation values are in good agreement. The MCNP calculation is available to sky-shine radiation dose calculation from Turbine Building with better accuracy. (author)

[en] Here, nucleoplasmin (Npm) is a highly conserved histone chaperone responsible for the maternal storage and zygotic release of histones H2A/H2B. Npm contains a pentameric N-terminal core domain and an intrinsically disordered C-terminal tail domain. Though intrinsically disordered regions are common among histone chaperones, their roles in histone binding and chaperoning remain unclear. Using an NMR-based approach, here we demonstrate that the Xenopus laevis Npm tail domain controls the binding of histones at its largest acidic stretch (A2) via direct competition with both the C-terminal basic stretch and basic nuclear localization signal. NMR and small-angle X-ray scattering (SAXS) structural analyses allowed us to construct models of both the tail domain and the pentameric complex. Functional analyses demonstrate that these competitive intramolecular interactions negatively regulate Npm histone chaperone activity in vitro. Together these data establish a potentially generalizable mechanism of histone chaperone regulation via dynamic and specific intramolecular shielding of histone interaction sites.

[en] α-Amino-β-carboxymuconate-ϵ-semialdehyde decarboxylase (ACMSD) plays an important role in L-tryptophan degradation via the kynurenine pathway. ACMSD forms a homodimer and is functionally inactive as a monomer because its catalytic assembly requires an arginine residue from a neighboring subunit. However, how the oligomeric state and self-association of ACMSD are controlled in solution remains unexplored. In this study, we demonstrate that ACMSD from Pseudomonas fluorescens can self-assemble into homodimer, tetramer, and higher-order structures. Using size-exclusion chromatography coupled with small-angle X-ray scattering (SEC-SAXS) analysis, we investigated the ACMSD tetramer structure, and fitting the SAXS data with X-ray crystal structures of the monomeric component, we could generate a pseudo-atomic structure of the tetramer. This analysis revealed a tetramer model of ACMSD as a head-on dimer of dimers. We observed that the tetramer is catalytically more active than the dimer and is in equilibrium with the monomer and dimer. Substituting a critical residue of the dimer–dimer interface, His-110, altered the tetramer dissociation profile by increasing the higher-order oligomer portion in solution without changing the X-ray crystal structure. ACMSD self-association was affected by pH, ionic strength, and other electrostatic interactions. Alignment of ACMSD sequences revealed that His-110 is highly conserved in a few bacteria that utilize nitrobenzoic acid as a sole source of carbon and energy, suggesting a dedicated functional role of ACMSD's self-assembly into the tetrameric and higher-order structures. Finally, these results indicate that the dynamic oligomerization status potentially regulates ACMSD activity and that SEC-SAXS coupled with X-ray crystallography is a powerful tool for studying protein self-association.

[en] A set of quantitative techniques is suggested for assessing SAXS data quality. These are applied in the form of a script, SAXStats, to a test set of 27 proteins, showing that these techniques are more sensitive than manual assessment of data quality. Small-angle X-ray scattering (SAXS) has grown in popularity in recent times with the advent of bright synchrotron X-ray sources, powerful computational resources and algorithms enabling the calculation of increasingly complex models. However, the lack of standardized data-quality metrics presents difficulties for the growing user community in accurately assessing the quality of experimental SAXS data. Here, a series of metrics to quantitatively describe SAXS data in an objective manner using statistical evaluations are defined. These metrics are applied to identify the effects of radiation damage, concentration dependence and interparticle interactions on SAXS data from a set of 27 previously described targets for which high-resolution structures have been determined via X-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy. The studies show that these metrics are sufficient to characterize SAXS data quality on a small sample set with statistical rigor and sensitivity similar to or better than manual analysis. The development of data-quality analysis strategies such as these initial efforts is needed to enable the accurate and unbiased assessment of SAXS data quality