Helix–coil dynamics of a Z-helix hairpin

✍ Scribed by J. Antosiewicz; M. W. German; J. H. Van De Sande; D. Porschke

• Book ID: 101718943
• Publisher: Wiley (John Wiley & Sons)
• Year: 1988
• Tongue: English
• Weight: 474 KB
• Volume: 27
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360270810

✦ Synopsis

Synopsis

The helix-coil transition of a Z-helix hairpin formed from d(C-G),T,(C-G), has been characterized by equilibrium melting and temperature jump experiments in 5M NaC10, and 10 mM Na,HPO,, pH 7.0. The melting curve can be represented by a simple all-or-none transition with a midpoint at 81.6 * 0.4OC and an enthalpy change of 287 k 15 kJ/mole. The temperature jump relaxation can be described by single exponentials at a reasonable accuracy. Amplitudes measured as a function of temperature provide equilibrium parameters consistent with those derived from equilibrium melting curves. The rate constants of Z-helix formation are found in the range from 1800 s-' a t 70°C to 800 s-' at 90°C and are assoCiated with an activation enthalpy of -(50 * 10) kJ/mole, whereas the rate constants of helix dissociation are found in the range from 200 s-' at 70°C to 4500 s-' at 90°C with an activation enthalpy +235 kJ/mole. These parameters are consistent with a requirement of 3-4 base pairs for helix nucleation. Apparently nucleation occurs in the Z-helix conformation, because a separate slow step corresonding to a B to Z transition has not been observed. In summary, the dynamics of the Z-helix-coil transition is very similar to that of previously investigated right-handed double helices.