Z-DNA

Z-DNA又稱Z型DNA，是DNA雙螺旋結構的一種形式，具有左旋型態的雙股螺旋（與常見的B-DNA相反），並呈現鋸齒形狀。Z-DNA為三種具生物活性的DNA雙螺旋結構之一，另兩種為A-DNA與B-DNA。

歷史[編輯]

Z-DNA為首先於1979年被解出晶體結構的DNA型態，研究者為麻省理工大學的Alexander Rich等人^[1]。B型及Z型相互結合時的結晶則解於2005年^[2]，使科學家了解Z-DNA在細胞中的潛在角色，當一段Z-DNA形成時，其兩端必為B-Z相互結合型態，形成與B-DNA的介面。

Z-DNA的雙股螺旋為左旋型態，與B-DNA的右旋型態明顯有所差別。其結構每兩個鹼基對重複出現一次。大小螺旋凹槽之間的差別較A型及B型小，只在寬度上有些微差異。這種型態並不常見，但某些特定情況可增加其存在的可能，如嘌呤-嘧啶交替序列、DNA超螺旋，或鹽份與某些陽離子濃度高時。

Z-DNA能夠與B-DNA構成相互結合型態，這種結構會使一對鹼基突出於雙螺旋之外。

幾何屬性	A-DNA	B-DNA	Z-DNA
螺旋方向	右旋	右旋	左旋
重複單元	1 bp	1 bp	2 bp
Rotation/bp	32.7°	35.9°	60°/2
bp/turn	10	11	12
Inclination of bp to axis	+19°	−1.2°	−9°
Rise/bp along axis	2.3 Å (0.23 nm)	3.32 Å (0.332 nm)	3.8 Å (0.38 nm)
Pitch/turn of helix	28.2 Å (2.82 nm)	33.2 Å (3.32 nm)	45.6 Å (4.56 nm)
Mean propeller twist	+18°	+16°	0°
糖基角度	anti	anti	C: anti, G: syn
Sugar pucker	C3'-endo	C2'-endo	C: C2'-endo, G: C3'-endo
直徑	23 Å (2.3 nm)	20 Å (2.0 nm)	18 Å (1.8 nm)
來源:^[3]^[4]^[5]

^ Wang AHJ, Quigley GJ, Kolpak FJ, Crawford JL, van Boom JH, Van der Marel G, Rich A. Molecular structure of a left-handed double helical DNA fragment at atomic resolution. Nature (London). 1979, 282: 680–686. PMID 514347
^ Ha SC, Lowenhaupt K, Rich A, Kim YG, Kim KK. Crystal structure of a junction between B-DNA and Z-DNA reveals two extruded bases. Nature. 2005, 437: 1183–1186. PMID 16237447.
^ Sinden, Richard R. DNA structure and function 1st. Academic Press. 1994-01-15: 398. ISBN 0-126-45750-6.
^ Rich A, Norheim A, Wang AHJ. The chemistry and biology of left-handed Z-DNA. Annual Review of Biochemistry. 1984, 53 (1): 791–846. PMID 6383204. doi:10.1146/annurev.bi.53.070184.004043.
^ Ho PS. The non-B-DNA structure of d(CA/TG)n does not differ from that of Z-DNA. Proc Natl Acad Sci USA. 1994-09-27, 91 (20): 9549–9553. Bibcode:1994PNAS...91.9549H. PMC 44850 . PMID 7937803. doi:10.1073/pnas.91.20.9549.

Sinden RR (1994). DNA structure and function. Academic Press, 179-216. ISBN 978-0-12-645750-6
Rich A, Zhang S (2003). Timeline: Z-DNA: the long road to biological function. Nat Rev Genet, 4:566–572.