Lowman H, Bina M
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907.
Biopolymers. 1990;30(9-10):861-76. doi: 10.1002/bip.360300902.
Previous studies demonstrated 16 well-defined nucleosome locations (A-P) on a tandemly repeated prototype 234 base pair (bp) mouse satellite repeat unit. We have aligned the A-P fragments to search for DNA sequence elements that might contribute to nucleosome placement at these positions. Our results demonstrate a strikingly regular, uninterrupted, periodic pattern for the AA dinucleotide occurrences along the entire length of the aligned fragments. The periodicity of the AA occurrences is about 9.7 bp. The pattern exhibits a local minimum at position 74, near the nucleosome dyad axis of symmetry. Other dinucleotides--including AC: GT, CA: TG, and CC: GG--are also placed periodically, but their patterns of occurrence are less regular and less frequent than AA. The calculated spacings between consecutive preferred nucleosome locations on mouse satellite DNA are nearly identical, corresponding to multiples of 9.7 bp. The correlation between the periodicity of dinucleotide occurrences and the average spacing of nucleosome positions suggests that the preferred nucleosome locations recur at intervals that may correspond to the DNA helical repeat in the mouse satellite nucleosomes, and that the histone octamers sample (or slip along) the duplex in steps of 9.7 bp during nucleosome formation on mouse satellite DNA.
先前的研究表明，在一个串联重复的、原型为234碱基对（bp）的小鼠卫星重复单元上存在16个明确的核小体位置（A - P）。我们已将A - P片段进行比对，以寻找可能有助于这些位置核小体定位的DNA序列元件。我们的结果表明，在比对片段的整个长度上，AA二核苷酸出现的模式具有显著的规则性、不间断性和周期性。AA出现的周期约为9.7 bp。该模式在靠近核小体二分对称轴的74位处呈现局部最小值。其他二核苷酸——包括AC:GT、CA:TG和CC:GG——也呈周期性排列，但其出现模式不如AA规则，频率也较低。计算得出的小鼠卫星DNA上连续的优选核小体位置之间的间距几乎相同，对应于9.7 bp的倍数。二核苷酸出现的周期性与核小体位置的平均间距之间的相关性表明，优选的核小体位置以可能对应于小鼠卫星核小体中DNA螺旋重复的间隔重复出现，并且在小鼠卫星DNA上形成核小体的过程中，组蛋白八聚体以9.7 bp的步长对双链进行采样（或沿双链滑动）。
