Z-DNA
Z-DNA is one of several possible structural forms of DNA . It is a left-handed double helix (in contrast to the B-shape common in nature , which forms a right-handed helix). Probably the Z-DNA together with the A- and B-DNA is one of the three biologically active forms of DNA.
history
Pohl and Jovin dealt with the connection between Z-DNA and B-DNA in their early work. They were able to show that the circular dichroism , CD for short, of poly (dG-dC) was almost completely reversible using 4 M NaCl solution. The assumption that this was caused by a conversion from B-DNA to Z-DNA was later confirmed by Raman spectroscopy of Z-DNA crystals in the solution. The Z-DNA itself was discovered as the first crystalline DNA structure by Alexander Rich , Andrew Wang and colleagues at MIT in 1979 (see X-ray diffraction ). However, a crystal structure was only reported in 2005, which shows Z-DNA directly in connection with B-DNA and thus provides indications of a biological activity of Z-DNA.
structure
The name Z-DNA is derived from the zigzag shape of the sugar-phosphate backbone. The structure is very different compared to the right-handed B-DNA. The Z-DNA is left-handed and has a structure that repeats itself every two base pairs (dimers). However, the Z-DNA is a metastable conformation of the DNA and is only used under certain circumstances (e.g. alternating pyrimidines / purines , high salt concentrations or DNA supercoiling ).
function
It is believed that Z-DNA u. a. plays a role during DNA transcription when there is a particularly large amount of supercoiled DNA . It was also observed that the presumed presence of Z-DNA coincides with transcriptional activity and it has been postulated that Z-DNA plays a role in the regulation of transcription.
| Structural feature | A-DNA | B-DNA | Z-DNA |
|---|---|---|---|
| helical sense of rotation | right | right | Left |
| diameter | ≈26 Å | ≈20 Å | ≈18 Å |
| Base pairs per helical turn | 11.6 | 10.4 ... 10.6 | 12 (6 dimers ) |
| Helical turn per base pair (twist) | 31 ° | 36 ° | 60 ° (per dimer ) |
| Pitch (increase per turn) | 34 Å | 34 Å | 44 Å |
| Increase per base | 2.9 Å | 3.4 Å | 7.4 Å (per dimer ) |
| Inclination angle of the base pairs to the axis | 20 ° | 6 ° | 7 ° |
| Big furrow | tight and deep | wide and deep | flat |
| Small furrow | wide and flat | tight and deep | tight and deep |
| Sugar conformation | C3'- endo | C2'- endo |
Pyrimidines : C2'- endo Purines : C3'- endo |
| Glycosidic bond | anti | anti |
Pyrimidines : anti purines : syn |
literature
- Donald Voet, Judith G. Voet: Biochemistry . 4th edition. John Wiley & Sons, Hoboken 2011, ISBN 978-0-470-57095-1 .
Web links
- ChemgaPedia images
swell
- ↑ FM Pohl, TM Jovin: Salt-induced co-operative conformational change of a synthetic DNA: equilibrium and kinetic studies with poly (dG-dC) . In: Journal of Molecular Biology . tape 67 , no. 3 , June 28, 1972, p. 375-396 , PMID 5045303 .
- ↑ TJ Thamann, RC Lord, AH Wang, A. Rich: The high salt form of poly (dG-dC) • poly (dG-dC) is left-handed Z-DNA: Raman spectra of crystals and solutions . In: Nucleic Acids Research . tape 9 , no. 20 , October 24, 1981, pp. 5443-5457 , PMID 7301594 .
- ↑ 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 . In: Nature (London) . 282, 1979, pp. 680-686. PMID 514347 .
- ↑ a b Sung Chul Ha, Ky Lowenhaupt, Alexander Rich, Yang-Gyun Kim, Kyeong Kyu Kim: Crystal structure of a junction between B-DNA and Z-DNA reveals two extruded bases . In: Nature . tape 437 , no. 7062 , October 20, 2005, p. 1183-1186 , doi : 10.1038 / nature04088 , PMID 16237447 .
- ↑ P. Christoph Champ, Sandor Maurice, Jeffrey M. Vargason, Tracy Camp, P. Shing Ho: Distributions of Z-DNA and nuclear factor I in human chromosome 22: a model for coupled transcriptional regulation . In: Nucleic Acids Research . tape 32 , no. 22 , 2004, p. 6501-6510 , doi : 10.1093 / nar / gkh988 , PMID 15598822 .