Structure of the DNA of bacteriophage ΦX174: V. Purine sequences

Abstract

Methods are described for the preparation of DNA, specifically labeled with carbon-14 in the purines, from bacteriophage ΦX174. This DNA, mixed with unlabeled calf thymus DNA as a carrier, has been degraded to purine tracts by hydrazinolysis and subsequent alkaline hydrolysis. The purine tracts have been separated according to magnitude by chromatography on a column of DEAE-Sephadex, at 55°C in the presence of 7 M -urea. The proportions of purines from calf thymus DNA, found in tracts of all magnitudes up to twelve, agree well with the previously measured proportions of pyrimidines in corresponding tracts, as would be expected from the complementary DNA structure. The complementarity restriction does not apply to ΦX DNA, and there appear to be purine tracts of greater length than any pyrimidine tract. A significant discrepancy has appeared between the numbers of purine and pyrimidine tracts, particularly between the numbers of solitary adenines and thymines. This may indicate an unsuspected flaw in these methods or an unusual feature in the structure of ΦX DNA.