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Abstract：
Noncrystallographic symmetry (NCS) averaging following molecular-replacement phasing is generally the major technique used to solve a structure with several molecules in one asymmetric unit, such as a spherical icosahedral viral particle. As an alternative method to NCS averaging, a new approach to optimize or to refine the electron density directly under NCS constraints is proposed. This method has the same effect as the conventional NCS-averaging method but does not include the process of Fourier synthesis to generate the electron density from amplitudes and the corresponding phases. It has great merit for the solution of structures with limited data that are either twinned or incomplete at low resolution. This method was applied to the case of the T = 1 shell-domain subviral particle of Penaeus vannamei nodavirus with data affected by twinning using the REFMAC5 refinement software.
摘要：
分子置换定相之后的非晶体学对称性（NCS）平均通常是用于解决一个不对称单元中具有多个分子的结构的主要技术。例如球形二十面体病毒颗粒。作为NCS平均的替代方法，提出了一种直接在NCS约束下优化或细化电子密度的新方法。该方法具有与常规NCS平均法相同的效果,但不包括从振幅和相应相位产生电子密度的傅立叶合成过程。对于具有有限数据的结构的解决方案具有很大的优点，这些数据在低分辨率下是配对的或不完整的。使用REFMAC5细化软件，将该方法应用于南美白对虾的T=1壳结构域亚病毒颗粒的情况，其数据受孪生影响。
