Acid degradation products of deoxyribonucleic acid

Abstract

The acid hydrolysis of calf thymus DNA by normal HCl at 100° results primarily in nucleotides containing one more phosphate than pyrimidine, a number of which have been isolated and identified by ion-exchange chromatography. This is consistent with an elimination mechanism that leaves on the pyrimidine residue those phosphates formerly lying between purine and pyrimidine residues. It also indicates that the loss of purine residues is a necessary prerequisite to the rupture of the polynucleotide chain by mild acidic hydrolysis. The presence of nucleotides containing equal amounts of pyrimidine and phosphate may be caused by the hydrolysis of phosphate from the initial products. About 33% of the phosphate appears as inorganic phosphate after 1 hour of hydrolysis; the bulk of this appears to be phosphate originally lying between purine residues in the original DNA. There is a slow rise to a new plateau of 50% at 3 to 4 hours. The sum of inorganic plus monoesterified phosphate remains constant from 1 hour to 4 hours, indicating a slow hydrolysis of monoester phosphate, presumably from the 3′ positions. The presence of all varieties of mono-, di-, and trinucleotide sequences that are possible from cytidylic and thymidylic acids indicates that all possible sequences of pyrimidine and of purine nucleotides exist in thymus DNA.