The left - handed dou

The con ver sion of right-handed dsDNA and dsRNA to the left-handed Z-con-formation in volves a re or ga ni za tion of the nu cleo tides rel a tive to each other. This con-ver sion can be fa cil i tated by the tight bind ing of a Z-conformation-specific pro tein domain from the ed it ing en zyme dsRNA adenosine deaminase. This may in flu ence the mod i fi ca tion of both pre-mRNAs as well as some rep li cat ing RNA vi ruses. Both DNA and RNA form sta ble dou ble he li-ces held to gether by Wat son-Crick base pairs. How ever, the pres ence of an added ox y gen atom in the back bone of RNA re sults in a con-sid er able change in the ge om e try of the mol e-cule. The B-DNA mol e cule has both ma jor and mi nor grooves, with the ma jor groove fully ac-ces si ble. On the other hand, A-RNA, be cause of the al tered pucker of the ribose ring, forms a dou ble he lix in which the mi nor groove is quite ac ces si ble, but the ma jor groove is constricted so that it is al most in ac ces si ble to neigh bor ing mol e cules. Right-handed B-DNA and A-RNA are the most sta ble forms of these du plexes. Both of these con for ma tions can be trans formed with the in put of en ergy into left-handed dou ble he li cal con for ma tions, which are still held to gether by Wat son-Crick base pairs, but with the back bones in an unusual zigzag shape, hence the name " Z "-con-for ma tion. This con tor tion of the back bone occurs be cause in the Z-conformation, the puckers of the furanose sugar rings in the polynucleotide chain al ter nate be tween that found in B-DNA (C2¢ endo) and that found in A-RNA (C3¢ endo). It is this al ter na tion that Pres ented at the In ter na tional Con fer ence on " Mo lec u lar Ar chi tec ture of Evo lu tion, Pri mary and Second ary De ter mi nants " Poznañ, Po land, Oc to ber 29–31, 2000.