Box C/D guide RNAs are abundant noncoding RNAs that primarily function to direct the 2-O-methylation of specific nucleotides by base-pairing with substrate RNAs. In archaea, a bipartite C/D RNA assembles with L7Ae, Nop5, and the methyltransferase fibrillarin into a modification enzyme with unique substrate specificity. Here, we determined the crystal structure of an archaeal C/D RNAprotein complex (RNP) composed of all 3 core proteins and an engineered half-guide RNA at 4 Å resolution, as well as 2 protein substructures at higher resolution. The RNP structure reveals that the C-terminal domains of Nop5 in the dimeric complex provide symmetric anchoring sites for 2 L7Ae-associated kink-turn motifs of the C/D RNA. A prominent protrusion in Nop5 seems to be important for guide RNA organization and function and for discriminating the structurally related U4 snRNA. Multiple conformations of the N-terminal domain of Nop5 and its associated fibrillarin in different structures indicate the inherent flexibility of the catalytic module, suggesting that a swinging motion of the catalytic module is part of the enzyme mechanism. We also built a model of a native C/D RNP with substrate and fibrillarin in an active conformation. Our results provide insight into the overall organization and mechanism of action of C/D RNA-guided RNA methyltransferases.crystal structure ͉ methylation ͉ RNA-protein complex ͉ non-coding RNA M ore than 100 types of chemical modification are introduced at specific sites of cellular RNAs after their transcription (1). These modifications, which greatly increase the chemical diversity of RNA, are generally beneficial and sometimes even critical for the structure and function of host RNAs. RNA modifications are normally carried out by individual protein enzymes. However, an exception is the large number of pseudouridine and 2Ј-O-methylated nucleotides in rRNAs, snRNAs, and tRNAs that are synthesized by H/ACA and C/D RNA-protein complexes (RNPs), respectively (2-6). In each such complex, a distinct guide RNA belonging to the H/ACA or C/D RNA family determines the substrate specificity by basepairing with the substrate around the modification site. These 2 classes of RNA-guided RNA modification enzymes are ubiquitous in eukaryotic and archaeal organisms but are not found in bacteria.The methylation guide C/D RNAs contain a C box (RUG-AUAG, R is purine) near the 5Ј end and a D box (CUGA) near the 3Ј end, and related boxes CЈ and DЈ at the internal region. One or 2 antisense sequences are present upstream of boxes D and DЈ and form a 10-21-bp duplex with the substrate, thereby selecting the nucleotide paired to the fifth nucleotide upstream of box D/DЈ for modification (7-9). Boxes C and D combine and fold into a kink-turn (K-turn) structural motif (10-13). A canonical K-turn is composed of 2 bent stems linked by a 3-nt bulge with an extruded nucleotide. One stem contains tandem sheared G⅐A pairs (hereafter called the GA-stem, also known as stem II or noncanonical stem), and the other contains WatsonCrick p...

To investigate the deflagration characteristics of CH4‐air mixture in confined space, fluid dynamic software Fluidyn was used to build numerical models that each consisted of a horizontal pipe and vertical branches to study the influence of different numbers of branch pipes on the deflagration propagation characteristics of CH4. Research findings suggested that the oscillation trend of the time history curve of pressure at the test point weakened and the peak initial deflagration pressure attenuated in an approximately linear manner with the increase of the propagation distance in the horizontal pipe. With the increase of the number of branches, the peak initial deflagration pressure at the same test point declined with an increasing amplitude. The vertical branch was found to have both “boosting” and “inhibiting” effects on flame propagation. And the inhibiting effect dominated as the number of vertical branches increased, which caused the flame propagation velocity within the horizontal pipe to significantly attenuate. In addition, the functions of the peak initial deflagration pressure varying with the number of branches and propagation distance in the horizontal pipe were obtained by fitting. According to the functions, the vertical branch had marked pressure venting effect on deflagration pressure in the horizontal pipe; the more the branch pipes were, the more significant the pressure venting effect was.

In this study, under the open-close conditions of a roadway outlet, the nonlinear dynamic analysis finite element program ANSYS/LS-DYNA was used to build models of explosions on roadways with 0˚ and 90˚ bending angles, to compare and analyse the shock wave propagation characteristics and variation laws. Moreover, the destructive effect of the explosion on the partition was analysed based on the level of damage caused to the human body by shock wave overpressure. The results show that the bending angle has an impact on the space-time distribution law of the explosion shock waves on the roadway. As the bending angle increases, the peak overpressure attenuation of the shock waves becomes prominent, and the arrival time for the same distance increases. The closure of the roadway outlet has a distance effect on the peak overpressure of the shock waves. The explosion shock waves cause the peak overpressure to rise sharply owing to the reflection and stacking effects near the closure. In the far zone of the outlet, the attenuation of the shock waves is too fast and has minimal impact on the peak overpressure. Additionally, overall, the closure of the roadway outlet increases the damage range of the explosion shock waves and the severity of their effect on the human body. With an increase in the bending angle, the damage range and severity decrease. These results can provide a reference for explosion disaster evaluation and prevention.

In this study, under the open-close conditions of a roadway outlet, ANSYS/LS-DYNA was used to build models of explosions on roadways with 0° and 90° bending angles, to compare and analyze the shock wave propagation characteristics and variation laws. Combined with the damage degree classification of shock wave overpressure to human body, the destructive effect zoning of explosion in roadway under the condition of opening and closing of roadway entrance was studied. The results showed that as the bending angle increased, the peak overpressure attenuation of the shock waves became prominent, and the arrival time for the same distance increased. The closure of the roadway outlet had a distance effect on the peak overpressure of the shock waves. The explosion shock waves caused the peak overpressure to rise sharply owing to the reflection and stacking effects near the closure. In the far zone of the outlet, the attenuation of the shock waves was too fast and had minimal impact on the peak overpressure. In addition, the existence of the roadway closure increased the damage area and the severity of the blast wave to human body as a whole. With an increase in the bending angle, the damage range and severity decreased.

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