The dideoxy chain-termination method (1 ) involves enzymatic elongation of a oligonucleotide primer that is annealed to a single-stranded DNA template. Single-stranded DNA of bacteriophage M13 (2 ) or phagemid vectors (3 ) give the most consistently satisfactory sequencing data. However, denatured double-stranded plasmid DNA can also serve as a suitable template and can also yield several hundred nucleotides of sequence information per reaction.
