Z-DNA

Z-DNA is one of the various possible structural forms of DNA. It is a left-handed double helix (as opposed to the usual B-form in nature, forming a right-handed helix). Believed to be the Z-DNA, together with the A- and the B- DNA is a DNA of the three biologically active forms.

History

The relationship between Z-DNA and B-DNA Pohl and Jovin employed in early work. They could show that the circular dichroism, short CD of poly (dG -dC ) using 4 M NaCl solution was almost completely reversible. The assumption that the cause was a conversion from B-DNA to Z - DNA for later confirmed by Raman spectroscopy of Z-DNA crystals in the solution. The Z- DNA itself was the first crystalline structure of DNA by Alexander Rich, Andrew Wang and colleagues at MIT discovered in 1979 (see X-ray diffraction ). However, it has been reported only in the year 2005 on a crystal structure, which shows Z-DNA directly in a compound with B- DNA, and thus provides evidence of biological activity of Z- DNA.

Structure

The name Z-DNA is derived from the zigzag course of the sugar-phosphate backbone. The structure is very different compared to the right-handed B - DNA. Because the Z-DNA is left-handed and has a structure that every two base pairs repeats ( dimers). However, Z-DNA is a metastable conformation of the DNA and is used only under certain conditions ( such as alternating pyrimidine / purine, high salt concentration or DNA supercoiling ).

Function

It is believed that the Z- DNA, inter alia, play a role in transcription of the DNA, especially if a lot of DNA is supercoiled. It was also observed that the presumed presence of the Z- DNA coincident with the transcription activity and it has been postulated that the Z- DNA plays a role in the regulation of transcription.