The Use of Primed Synthesis by DNA Polymerase I to Study an Intercistronic Sequence of ΦX‐174 DNA

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Abstract
A decadeoxynucleotide complementary to ten nucleotides in the major ribosome‐protected fragment of ΦX‐174 plus‐strand DNA has been chemically ksynthesized and used as a primer for DNA Polymerase I on ΦX‐174 plus‐strand DNA as template. The sequence of the first 40 nucleotides incorporated onto the decadeoxynucleotide has been determined. This sequence extends further the sequence of the intercistronic region preceding gene G and shows the presence of another termination codon. The sequence was determined by using manganese as the activating cation for DNA polymerase I which allows ribonucleotides to be incorporated as well as deoxyribonucleotides. The ribo‐substituted product was then cleaved specifically at the ribonucleotide residues to generate a series of overlapping ribo‐terminated fragments whose sequences were sufficient to determine the complete sequence of the first 40 nucleotides. No evidence for misincorporation by DNA polymerase I in the presence of manganese was detected.