Cyclin-Dependent Kinase Activity Controls the Onset of the HCMV Lytic Cycle

The onset of human cytomegalovirus (HCMV) lytic infection is strictly synchronized with the host cell cycle. Infected G0/G1 cells support viral immediate early (IE) gene expression and proceed to the G1/S boundary where they finally arrest. In contrast, S/G2 cells can be infected but effectively block IE gene expression and this inhibition is not relieved until host cells have divided and reentered G1. During latent infection IE gene expression is also inhibited, and for reactivation to occur this block to IE gene expression must be overcome. It is only poorly understood which viral and/or cellular activities maintain the block to cell cycle or latency-associated viral IE gene repression and whether the two mechanisms may be linked. Here, we show that the block to IE gene expression during S and G2 phase can be overcome by both genotoxic stress and chemical inhibitors of cellular DNA replication, pointing to the involvement of checkpoint-dependent signaling pathways in controlling IE gene repression. Checkpoint-dependent rescue of IE expression strictly requires p53 and in the absence of checkpoint activation is mimicked by proteasomal inhibition in a p53 dependent manner. Requirement for the cyclin dependent kinase (CDK) inhibitor p21 downstream of p53 suggests a pivotal role for CDKs in controlling IE gene repression in S/G2 and treatment of S/G2 cells with the CDK inhibitor roscovitine alleviates IE repression independently of p53. Importantly, CDK inhibiton also overcomes the block to IE expression during quiescent infection of NTera2 (NT2) cells. Thus, a timely block to CDK activity not only secures phase specificity of the cell cycle dependent HCMV IE gene expression program, but in addition plays a hitherto unrecognized role in preventing the establishment of a latent-like state

NBC105: 2019 Seismic design of buildings in Nepal: New provisions in the code

The NBC 105: 2019 Seismic Design of Buildings in Nepal is the revised version of the original code for seismic design first published in 1994. The code has never been reviewed and updated since then till the moment. Recognizing the development in research and technology and new knowledge learnt from various large earthquakes in last 25 years, the Government of Nepal decided to initiate the first revision of the seismic design code. The objective of this revised standard is to provide designers with general procedures and criteria for the structural design of buildings prevalent in Nepal. This paper presents the basic features of the revision and the principles adopted in the standard. A new seismic hazard map of Nepal was proposed at the outset based on probabilistic format. Accordingly the PGA values for various locations of Nepal were revised. The performance requirements have been introduced precisely in terms of collapse prevention and damage limitation; there is a further recommendation to verify the performance requirements checking the ultimate limit state and serviceability limit state. It is proposed to check life safety and damage limitation performance requirements. Two different spectra are proposed for seismic coefficient method and modal response spectrum method. Four types of sub soil category are proposed. Very soft soil category is added in addition to previous three categories. This new soil category represents a very deep soft soil found in Kathmandu valley. Research has indicated that hard soil should have greater acceleration demand at smaller periods. This issue is rarely addressed in design codes internationally and the revised version of the NBC 105 is one of the first codes to accommodate this in practice. The revised code, retaining the linear analysis, introduces the non-linear methods of analysis. The empirical formulae for determination of fundamental translation period have been revised. Other principal changes include the importance classes and importance factors, load combinations and load factors. The Performance factor (K), which was used in the earlier version to obtain seismic coefficient, does not reflect the modern seismic design philosophy of reducing the elastic seismic forces. The response reduction factors (Ductility factor, R and Overstrength factor, ) are introduced. The horizontal base shear coefficient will be determined separately for ultimate limit state and serviceability limit state. The horizontal design spectrum for the modal response spectrum method has been given different for ultimate limit state and for serviceability limit state. A separate section on structural irregularity has been added. The revised code now requires checking the inter-story drift for both serviceability limit state and ultimate limit state. The standard has been developed in a new format considering the recent development in the research and technology as well as the lessons from the recent earthquakes. The whole document has been spread over 10 sections with 2 annexes separately for ductile detailing of structural concrete and structural steel

Probabilistic seismic hazard assessment of Nepal for revision of national building code NBC105

Being located in seismically active Himalayan mountain belt, Nepal has been the locus of many devastating earthquakes. The Mw 8.4 Bihar-Nepal earthquake of 1934 AD was the biggest earthquake disaster in Nepal that had highlighted the need of a building seismic design code for safer construction. Though the necessity was realised earlier, Nepal developed its first National Building Code (NBC-105) only in 1994 after the 1988 Mw 6.9Udayapur earthquake in eastern Nepal. In April 2015, central Nepal witnessed the Mw 7.8 Gorkha earthquake, which had epicentre at Barpak village of Gorkha district, about 75 km west of Kathmandu. The ground mtions recorded at soft soil sites in Kathmandu Valley clearly show strong site effect resulting in high energy in long period, i.e. at 3s to 5s. A comparative study has revealed that, at least in Kathmandu Valley, the observed ground motions exceeded the seismic design demand proposed by NBC-105 for some period ranges. Unsurprisingly, the earthquake caused extensive damage to buildings and infrastructures in 14 districts(mostly towards east of the epicentre due to further ruptured directivity effect) and killed 8,970 people. This earthquake also triggered revision of the existing national building code (known as NBC- 105)by the Government of Nepal.A key feature of the revision of NBC-105 has been re-assessment of national seismic hazard by adopting a probabilistic approach. Since the development of NBC-105 in 1994, a large number of studies have been carried on seismo-tectonics, active fault, paleoseismology, seismicity, geodesy etc, which have significantly increased the level of knowledge on seismic sources in the central Himalayas. In addition, after the 2015 Gorkha earthquake, much knowledge is gained on the geometry of the main seismogenic fault, the Main Himalayan Thrust (MHT) also called the Main Frontal Thrust (MFT) at the surface of the Himalayan front. Based on recent researches, in contrast to seismic sources adopted in 1994, a fault source (MHT) and area sources, i.e. northern garbens in Tibet, strike-slip event dominant sources in eastern and western Nepal and a source south of MHT are considered for seismic hazard analysis. As there is no specific Ground Motion Prediction Equation (GMPE) for the Himalayas, based on seismo-tectonics, GMPEs are adopted including Next Generation Attenuation laws. More than two GMPES are used for each source using the logic tree approach. Seismic hazard is computed for 2%, and 10% probability of exceedence in 50 year. In contrast to hazard map of 1994, the zones of relatively higher Peak Ground Acceleration (PGA) i.e. 0.36g to 0.46g are, for 10% probability of exceedence in 50 year, concentrated just above the locked portion of MHT throughout the country. The PGA values gradually decrease towards the north and south of MFT. This pattern of PGA distribution is consistent with the coupling nature of the MHT in the Himalayas

An Overlapping Kinase and Phosphatase Docking Site Regulates Activity of the Retinoblastoma Protein

The phosphorylation state and corresponding activity of the retinoblastoma tumor suppressor protein (Rb) are modulated by a balance of kinase and phosphatase activities. Here we characterize the association of Rb with the catalytic subunit of protein phosphatase 1 (PP1c). A crystal structure identifies an enzyme docking site in the Rb C-terminal domain that is required for efficient PP1c activity toward Rb. The phosphatase docking site overlaps with the known docking site for cyclin-dependent kinase (Cdk), and PP1 competition with Cdk-cyclins for Rb binding is sufficient to retain Rb activity and block cell-cycle advancement. These results provide the first detailed molecular insights into Rb activation and establish a novel mechanism for Rb regulation in which kinase and phosphatase compete for substrate docking