The structure of the DNA of bacteriophage φX174: IV. Pyrimidine sequences

Abstract

Apurinic acid was prepared from 14C-labeled DNA of the bacteriophage φX174 with unlabeled calf thymus DNA as carrier. The terminal phosphates of the pyrimidine tracts were removed by treatment with the alkaline phosphatase of E. coli and the resulting mixture fractionated on a column of DEAE-Sephadex into fragments of uniform chain length (isopliths) up to undecanucleotides. The distributions of isopliths in the DNAs of calf thymus and φX have been determined and compared with values calculated on the assumption that the pyrimidines are randomly distributed. The oligonucleotide tracts up to the hexanucleotide were further separated by paper chromatography into isomeric groups. Paper chromatography and paper electrophoresis have been used to isolate individual sequences of pyrimidines from the larger oligonucleotides in which the restrictions imposed by the genetic code and the size of the φX DNA molecule have reduced the number of possible isopliths to a very few. The nucleotide compositions and terminal dinucleotides of several of these sequences have been determined.