發(fā)表在BioMed Central開放期刊Cell & Bioscience 上的新研究，首次說明了左旋型的Z型DNA,，它通常只被發(fā)現(xiàn)于DNA被復(fù)制的地方,，也能在核小體上形成。
提供生命藍圖的DNA結(jié)構(gòu)曾被描述為一個雙螺旋,。為了節(jié)省細胞核內(nèi)空間,，DNA緊緊地纏繞形成核小體的蛋白質(zhì)，然后進一步纏繞,，壓縮成染色質(zhì),，接著壓縮成染色體,。但是，右手螺旋（也稱為B型DNA）的這種熟悉形象不是DNA的唯一形式,。在DNA被復(fù)制成RNA的位置（用作制造蛋白質(zhì)指令的信使）,，DNA需要解纏繞，在負超螺旋過程中,，能形成DNA雙螺旋的左手螺旋變體（Z-DNA）,。
最開始認為，Z-DNA只能在活性RNA聚合酶（組裝RNA的酶）存在下形成,。但是,，最近發(fā)現(xiàn)，SWI/SNF能將某些B-DNA序列轉(zhuǎn)換成Z-DNA,，其中SWI/SNF是一種參與重塑核小體和允許RNA聚合酶接近DNA的蛋白質(zhì),。
由Keji Zhao博士領(lǐng)導(dǎo)的研究小組發(fā)現(xiàn)，他們通過增加SWI/SNF 和 ATP（細胞能量來源）能將核小體上的B-DNA轉(zhuǎn)換成Z-DNA,，形成的Z-核小體是一種新結(jié)構(gòu),。
來自美國國立衛(wèi)生研究院的趙博士解釋說，"事實上,，我們在核小體上發(fā)現(xiàn)Z-DNA的事實是理解染色體重組與Z-DNA調(diào)節(jié)基因表達的作用的新一步,。然而，Z-核小體很可能是一個暫時結(jié)構(gòu),，但它為DNA結(jié)合蛋白配置提供了一個機會的窗口,，這可以招募、調(diào)節(jié)或阻止轉(zhuǎn)錄機制和蛋白表達,。"（生物谷bioon.com）
doi:10.1186/2045-3701-2-3
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SWI/SNF-mediated chromatin remodeling induces Z-DNA formation on a nucleosome
Niveen Mulholland, Yan Xu, Hiroshi Sugiyama, Keji Zhao
Abstract Background Z-DNA is a higher-energy, left-handed form of the double helix. A primary function of Z-DNA formation is to facilitate transcriptional initiation and activation. Sequences favoring Z-DNA formation are frequently located in promoter regions and Z-DNA is stabilized by torsional strain resulting from negative supercoiling, such as that generated by an actively transcribing polymerase or by a nucleosome remodeling event. We previously have shown that activation of the CSF1 gene by a chromatin remodeling event in the promoter results in Z-DNA formation at TG repeats within the promoter. Results We show that remodeling of a mononucleosome by the human SWI/SNF complex results in Z-DNA formation when the DNA within the mononucleosome contains Z-DNA favoring sequence. Nuclease accessibility patterns of nucleosome core particle consisting of Z-DNA are quite different from counterpart nucleosomes containing classic B-DNA. Z-nucleosomes represent a novel mononucleosome structure. Conclusions: We present evidence that Z-DNA can form on nucleosomes though previous observations indicate the occlusion of nucleosome formation from Z-DNA.
