THE SENDAI VIRUS NUCLEOCAPSID EXISTS IN AT LEAST 4 DIFFERENT HELICAL STATES
THE SENDAI VIRUS NUCLEOCAPSID EXISTS IN AT LEAST 4 DIFFERENT HELICAL STATES
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DOI：
10.1128/jvi.63.5.2233-2243.1989
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发表时间：
1989-05-01
影响因子：
5.4
通讯作者：
MURTI, G
中科院分区：
文献类型：
--
作者：
EGELMAN, EH;WU, SS;MURTI, G
仙台病毒核衣壳已通过电子显微镜观察到共存于三种不同的螺距构象，5.3，6.8和37.5 nm。5.3-和6.8-nm的构象都存在于醋酸铀酰负染色的制剂和钽钨金属阴影的制剂，而37.5-nm的构象，这是以前没有报道过的，只存在于阴影的制剂。5.3 nm间距构象似乎是两种离散结构状态的混合物，两者之间的结构扭曲差异很小。我们已经使用图像重建技术的平均数据集，从8个负染色的核衣壳产生一个三维重建在2.4 nm分辨率的结构中的一个5.3 nm的间距状态。在这种状态下，在螺旋的每一圈中有13.07个核衣壳蛋白（NP）亚基。螺旋重复是79.5 nm，包含196个亚基，在15圈的左手5.3 nm螺旋。亚基的排列产生了一个直径为5.0 nm的中空核，形成了一个内部螺旋槽。RNA约占核衣壳质量的3%，因此其位置在重建中并不明显。由于RNA在mRNA转录和基因组复制过程中仍然与NP亚基结合，因此核壳中的结构转变可能决定基因组对聚合酶的可及性。或者，我们已经重建的大的中空核心和内部螺旋槽可以允许进入RNA，即使在紧密卷曲的5.3 nm间距构象。
Sendai virus nucleocapsids have been observed by electron microscopy to coexist in three different helical pitch conformations, 5.3, 6.8 and 37.5 nm. The 5.3- and 6.8-nm conformations are present both in uranyl acetate negatively stained preparations and in tantalum-tungsten metal-shadowed preparations, whereas the 37.5-nm conformation, which has not been previously reported, is present only in the shadowed preparations. The 5.3-nm pitch conformation appears to be a mixture of two discrete structural states, with a small difference in the twist of the structure between the two. We have used image reconstruction techniques on an averaged data set from eight negatively stained nucleocapsids to produce a three-dimensional reconstruction at 2.4-nm resolution of the structure in one of the 5.3-nm pitch states. There are 13.07 nucleocapsid protein (NP) subunits in each turn of the helix in this state. The helical repeat is 79.5 nm, containing 196 subunits in 15 turns of the left-handed 5.3-nm helix. The arrangement of subunits produces a 5.0-nm-diameter hollow core which forms an internal helical groove. The RNA accounts for about 3% of the mass of the nucleocapsid, and so its location is not conspicuous in the reconstruction. Because the RNA remains associated with the NP subunits during mRNA transcription and genome replication, structural transitions in the nucleocapsid may determine the accessibility of the genome to polymerases. Alternatively, the large hollow core and internal helical groove we have reconstructed may allow access to the RNA even in the tightly coiled 5.3-nm pitch conformation.