The effect of hormones of DNA.

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Abstract
DNA from human placental nuclei was incubated with each of the following hormones (all at physiological serum concentrations): estrone, 17[beta]-estradiol, cortisol, insulin, somatotrophin, and epinephrine. Alteration of the melting profile of the DNA was used to assess the effect of the hormone on the strength of the DNA intrastrand bonds. All of the hormones studied caused a weakening of the bonds. 17[alpha] -estradiol (the biologically inactive isomer) and boiled somatotropin were inactive, as was L-thyroxine. A deoxyribonucleoprotein complex isolated from the nuclei of placental cells was affected by the hormones in the same way as pure DNA. Denatured DNA, sheared DNA, and DNA isolated from B. subtilis were all unaffected by the hormones. Two types of synthetic DNA, poly d(A[center dot]T) and poly d(G[center dot]C), also were not affected by the hormones, implying a need for stereospeciflc fit between hormones and DNA. One action of hormones is to activate genes by promoting the separation of complementary strands of specific segments of the DNA double helix prior to transcription.