Journal of Molecular Biology 1995-02-03

Poly(dA).poly(dT) forms very stable nucleosomes at higher temperatures.

H L Puhl, M J Behe

Index: J. Mol. Biol. 245(5) , 559-67, (1995)

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Abstract

The synthetic polymer poly(dA).poly(dT) was long thought to be refractory to nucleosome formation. Several years ago our laboratory demonstrated that the polymer could be mixed with authentic nucleosomes in a low-salt exchange procedure to form a nucleoprotein complex that behaved in a manner identical with that of nucleosomes. Competitive exchange assays at 37 degrees C showed that the homopolymer reconstituted about as well as heterogenous-sequence DNA. However, studies by other laboratories have shown that the conformation of poly(dA).poly(dT) depends on temperature; the polymer converts from its well-known, atypical structure, found at ambient temperature, to a conformation more closely resembling a canonical B form as temperature is increased. We have measured the ability of the homopurine.homopyrimidine to form nucleosomes as a function of temperature. It is seen that poly(dA).poly(dT) forms nucleosomes more strongly as the temperature of the exchange mixture is increased, so that poly(dA).(dT) outcompetes heterogeneous-sequence DNA for histones at elevated temperatures.