Protection of Deoxyribonucleic Acid from Nuclease Action by Histones.

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Abstract
Of the 5 main histone proteins present in chromatin, only the very lysine-rich histone F1 seems to function independently from other histones; histones F2A1, F2A2, F2B and F3 form a complex, which apparently has an octameric structure containing 2 copies of each histone. The arrangement of different histones in the oligomer was investigated by studying the capacity of different histones to protect DNA from nuclease action. The idea behind these experiments was that the histone species that protect DNA best are those that interact physically with DNA in the octamer, while those that protect DNA poorly are possibly not in direct association with DNA. Increasing amounts of total histones, or each histone protein separately, were incubated with the same amount of calf thymus DNA for 10 min, in order to allow the complex formation between DNA and histones to occur. After preincubation, the susceptibility of the DNA in these complexes to DNase I was examined. The DNA was protected to vaying degrees from enzymatic digestion by DNase, the extent of this protection being dependent on the histone employed. The lysine-rich histone F1 gave the best protection, while the arginine-rich histone protein F2A1 had the weakest effect. The F2A2 histone, which is a slightly lysine-rich protein, inhibited DNase action somewhat more effectively than the histones F2B and F3. The DNA protection capacity of the total histones was very similar to that of F2A2.

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