The Sanger dideoxy sequencing method is also known as the enzymatic method of DNA sequencing. It has been discovered in the 1970s and its modification is used until now.
This method is based on incorporation of modified bases - dideoxynucleotides, during DNA replication of the template strand. Incorporation of a dideoxynucleotide triggers DNA replication arrest and the DNA strand cannot be elongated any further.
In the first step of sequencing, the sequenced DNA is denaturated and labeled with a primer. This DNA is then added to four different tubes: each containing regular dNTP, a lower concentration of one specific ddNTP (ddATP, ddTTP, ddCTP, ddGTP) and a DNA polymerase. The strands are replicated and the elongation stops each time, when a ddNTP is incorporated. These fragments of DNA are after separated on a sequencing gel and analyzed.
Automatic DNA sequencing:
Is a modern version of Sanger's dideoxy sequencing method, in which the DNA synthesis occurs in one reaction and the elongated products are sorted by fluorescent labeling of the ddNTP. Each ddNTP has its own label. The fragments are then usually analyzed by kapilar electrophoresis by a laser beam.