Tetrahydrocortisol–apolipoprotein A-I complex specifically interacts with eukaryotic DNA and GCC elements of genes

Tetrahydrocortisol stimulates DNA and protein biosynthesis in hepatocytes only when it enters the complex with apolipoprotein A-I. Tetrahydrocortisol–apolipoprotein A-I (THC–apoA-I) complex specifically interacts with eukaryotic DNA isolated from rat liver. In the process of interaction, rupture of hydrogen bonds between the pairs of nitrous bases occurs with the formation of single-stranded DNA structures. In such state DNA forms complexes with DNA-dependent RNA-polymerase. The most probable site of binding the tetrahydrocortisol–apolipoprotein A-I complex with DNA is the sequence of CC(GCC) n type entering the structure of many genes, among them the structure of human apolipoprotein A-I gene. Oligonucleotide of this type has been synthesized. Association constant ( K ass) of it with tetrahydrocortisol–apolipoprotein A-I complex was shown to be 1.66×10 6 M −1. Substitution of tetrahydrocortisol for cortisol in the complex results in a considerable decrease of K ass. It was assumed that in the GC-pairs of the given sequence tetrahydrocortisol itself participates in the formation of hydrogen bonds with cytosine, favoring their rupture with complementary base—guanine.