STRUCTURE OF DNA OF BACTERIOPHAGE FD .I. ABSENCE OF NON-PHOSPHODIESTER LINKAGES

When the DNA from bacteriophage fd is treated first with an endonuclease and then with an exonuolease, all molecules resistant to exonucleolytic attack are circular molecules which have not received an endonucleolytic cut. In linear molecules no evidence could be found for a covalent bond which could not be cleaved by exonuclease I. A similar result was obtained for bacteriophage φX174,. The products of enzymic hydrolysis of highly 32P-labelled fd DNA were analysed by two-dimensional thin-layer chromatography, an assay which could detect as little as a single phosphorus atom per DNA molecule. Only the four common deoxynucleotides were found after extensive action of pancreatic DNase and venom phosphodiesterase. From these data it is concluded that fd DNA and φX DNA are continuous polynucleotide chains. © 1969.