Isolation of A·T-rich fragments from calf thymus DNA using the phenol method

Abstract

The action of phenol on the products of partial digestion of calf thymus DNA by K 2 DNAase causes a loss of 3–5% of the material passing into the phenol phase. This part of DNA can be regained in the aqueous phase by lowering both the temperature and the ionic strength. Among oligonucleotides up to 7 monomers in length, those which are soluble in phenol do not contain guanine residues. Phenol-soluble DNA fragments of the molecular weight of an order of 2000–50 000 appeared to be composed mainly of adenosine phosphate. They also contain some thymine and only traces of guanine and cytosine. Some longer A · T-rich fragments, even up to 5 · 10 6 daltons, were repeatedly found in the phenol phase, but their base composition has not been determined yet. The method presented here was found very convenient for the isolation of the relatively large A·T-rich DNA fragments. The property of DNA or its fragments to dissolve in phenol seems to be dependent on an adequate primary structure, probably similar to that of poly (dA-dT).