Automated DNA Sequencing Machine

 Genetic Analyzer 3130xl from Applied Biosystems International Incorporated,

Foster City, California, USA

DNA Sequencing Machine

Double stranded DNA is the carrier of genetic information in all living organisms. The DNA strand is made of just four nucleotides called adenine (A), thymine (T), guanine (G), and cytosine (C). The particular sequence in which these four nucleotides are present in the DNA, called the “DNA Sequence” is what decides its function. There a few DNA sequencing methods by which this “DNA Sequence” can be read. In 1980, Frederick Sanger received Noble Prize for devising one of such methods called chain termination method or ‘Sanger Method’. This method used radioactively labeled primer, dideoxy nucleotides, solid acrylamide gel, autoradiography and manual reading of the sequence from autoradiogram. In 1990s, this method was automated by using fluorescent nucleotides, semisolid gel capillaries and CCD camera.

In automated DNA sequencing, the sequencing reactions are made with the DNA to be sequenced, and kept in the Sequencing Machine. The machine itself loads the samples on capillaries and separates the fragments according to size. When the separated fragments cross the detection window at the bottom of the capillaries, the CCD camera detects if the fluorescent nucleotide is A or T or C or G, and in this way it continuously reads the DNA sequence. At the end, it gives a chromatogram and the corresponding text file of the DNA sequence. When the sequencing of the first sample is over, it cleans the capillary, fills fresh gel, loads the next sample, separates and detects the fragments and gives the DNA sequence. This will be repeated till it finishes all the samples. The automated DNA sequencing machine in our department has the capacity to sequence 16 DNA genes per hour while the manual method would take 8 days for the same.