Effect of Tetrahydrocortisol-Apolipoprotein A-I Complex on the Secondary Structure of Eukaryotic DNA and Its Interaction with RNA-Polymerase

L. E. Panin^*, O. I. Gimautdinova, P. A. Kuznetsov, M. V. Akimzhanova, and F. V. Tuzikov

Research Institute of Biochemistry, Siberian Branch of the Russian Academy of Medical Sciences, ul. Akademika Timakova 2, Novosibirsk, 630117 Russia; fax: (3832) 32-2735; E-mail: ibch@cyber.ma.nsc.ru

^* To whom correspondence should be addressed.

Received June 6, 2001; Revision received September 4, 2001

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The in vitro effect of tetrahydrocortisol-apolipoprotein A-I complex on native adult rat liver DNA results in the formation of S1 nuclease sensitive fragments that are irregularly distributed throughout a genome. Low-angle X-ray scattering showed that after the interaction with the tetrahydrocortisol-apolipoprotein A-I complex, DNA can bind to RNA-polymerase with a high and dose-dependent cooperativity. This indicates that the effect of tetrahydrocortisol-apolipoprotein A-I complex on secondary eukaryotic DNA structure causes a local denaturation of the double helix, promoting high cooperativity of binding to RNA-polymerase. The reduced form of the hormone, tetrahydrocortisol, previously considered as an inactive metabolite, when complexed with apolipoprotein A-I, promotes a biological function similar to that of a transcription factor.

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KEY WORDS: DNA secondary structure, apolipoprotein A-I, tetrahydrocortisol, S1-nuclease, RNA-polymerase, low-angle X-ray scattering

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