Z-RNA

Z-RNA is a left-handed alternative conformation for the RNA double helix. Just like for Z-DNA, Z-RNA is favored by a sequence composed of Purine/Pyrimidine repeats and especially CG repeats.

Discovery

The ability of dsRNA to convert into a left-handed helix was demonstrated using NMR and circular dichroism in 1984.^[1] This conversion was shown to require high ionic strength and elevated temperatures (35 degrees).

Structural characteristics

Z-RNA to resemble, but not be identical, to that of Z-DNA.^[2] The structure of the complex of a Zalpha domain with Z-RNA under close to physiological salt concentrations however suggests a structure much closer to the Z-DNA conformation and points to two forms of Z-RNA (low and high salt conformations) ^[3]

Role in biology

Formation of Z-RNA in living cells was suggested by experiments using anti-Z-RNA antibodies to stain fixed protozoan cells ^[4] Further evidence accrued with the discovery that the Zalpha domain of the RNA editing enzyme ADAR1 binds and recognizes with high affinity Z-RNA.^[5] Structural features of the recognition of Z-RNA by Zalpha domains were revealed by the crystallographic study of the complex ^[3]

References

1. Hall, K., P. Cruz, I. Tinoco, Jr., T.M. Jovin, and J.H. van de Sande, 'Z-RNA'--a left-handed RNA double helix. Nature, 1984. 311(5986): p. 584-6.
2. Popenda, M., J. Milecki, and R.W. Adamiak, High salt solution structure of a left-handed RNA double p. 4044-54.
3. Placido, D., B.A. Brown, 2nd, K. Lowenhaupt, A. Rich, and A. Athanasiadis, A left-handed RNA double helix bound by the Z alpha domain of the RNA-editing enzyme ADAR1. Structure, 2007. 15(4): p. 395-404.
4. 1. Zarling, D.A., C.J. Calhoun, C.C. Hardin, and A.H. Zarling, Cytoplasmic Z-RNA. Proc Natl Acad Sci U S A, 1987. 84(17): p. 6117-21.
5. Brown, B.A., 2nd, K. Lowenhaupt, C.M. Wilbert, E.B. Hanlon, and A. Rich, The Zalpha domain of the editing enzyme dsRNA adenosine deaminase binds left-handed Z-RNA as well as Z-DNA. Proc Natl Acad Sci U S A, 2000. 97(25): p. 13532-6.