Pyrimidine tract analysis of the deoxyribonucleic acid of chick embryo lethal orphan virus

Abstract

Pyrimidine tracts released from 32P-labelled chick embryo lethal orphan (CELO) virus DNA by formic acid-diphenylamine degradation were fractionated according to chain length by chromatography on DEAE-cellulose at pH 5.5. Isostichs (pyrimidine oligonucleotide tracts of a given length) of 1–13 pyrimidine residues were identified, and their amounts were estimated. Some tracts of 15 or 16 residues were also detected but could not be characterized further. The pyrimidine isostichs were then subfractionated into their components (i.e., tracts of equal length but different cytosine: thymine ratios). Isostichs 1–8 had all possible components, isostich 9 had 9 components, and isostichs 10 and 11 each had 8. CELO virus DNA contained a cytosine tract of 8 residues and another of 9 residues, and 2 tracts of 10 thymine residues, none of which have been found in DNA from other sources. The frequencies of isostich components in CELO virus DNA were compared with those expected in a random polymer of the same base composition by plotting the contribution of each isostich component to the total x 2. Similar plots were made from published data on DNA from other sources. Each DNA had a characteristic pattern different from that obtained with CELO virus DNA. The patterns for bacteriophage lambda and Escherichia coli were similar.