Blasquez V, Stein A, Ambrose C, Bina M
J Mol Biol. 1986 Sep 5;191(1):97-106. doi: 10.1016/0022-2836(86)90425-0.
We have investigated the average nucleosome spacing in the chromatin from several simian virus 40 virion assembly mutants temperature-sensitive in the major capsid protein VP1. Viral assembly intermediates that accumulate in cells infected with mutants that block virion assembly at the propagation step (tsB) have an average nucleosome repeat length similar to that of wild-type SV40 chromatin, approximately 198(+/- 4) base-pairs. This repeat length is longer than that of the host (BSC-40) cellular chromatin, which has a value of 187(+/- 4) base-pairs. In contrast, SV40 chromatin from cells infected with virus containing a mutation that blocks virion assembly at the initiation step (tsC) has a significantly shorter average repeat length of 177(+/- 4) base-pairs. At the permissive temperature (33 degrees C), tsC chromatin has a nucleosome spacing periodicity essentially the same as that of wild-type SV40 chromatin. In addition to possessing a chromatin structure with nucleosomes that are, on the average, closer together, tsC chromatin contains a nuclease-hypersensitive or open region in nearly all molecules, but apparently the same number of nucleosomes. These findings suggest that nucleosomes are deposited initially on newly replicated SV40 chromatin in such a way as to leave the DNA region containing the origin of replication and transcription enhancers uncovered. Subsequent interaction with capsid proteins appears to increase the average nucleosome spacing and consequently to cover the open region for encapsidation.
我们研究了来自几种在主要衣壳蛋白VP1中温度敏感的猿猴病毒40病毒体组装突变体的染色质中的平均核小体间距。在感染了在传播步骤（tsB）阻断病毒体组装的突变体的细胞中积累的病毒组装中间体，其平均核小体重复长度与野生型SV40染色质相似，约为198（±4）个碱基对。这个重复长度比宿主（BSC - 40）细胞染色质的重复长度长，宿主细胞染色质的值为187（±4）个碱基对。相比之下，感染了在起始步骤（tsC）阻断病毒体组装的病毒的细胞中的SV40染色质，其平均重复长度明显更短，为177（±4）个碱基对。在允许温度（33℃）下，tsC染色质的核小体间距周期性与野生型SV40染色质基本相同。除了具有核小体平均间距更近的染色质结构外，tsC染色质在几乎所有分子中都含有一个核酸酶超敏感或开放区域，但核小体数量显然相同。这些发现表明，核小体最初以这样一种方式沉积在新复制的SV40染色质上，即让包含复制起点和转录增强子的DNA区域不被覆盖。随后与衣壳蛋白的相互作用似乎增加了平均核小体间距，从而覆盖了用于衣壳化的开放区域。
