[Gene technology in clinical medicine--DNA sequencing].

There are two established procedures for sequencing cloned DNA fragments. In Maxam-Gilbert sequencing, or sequencing by chemical degradation, end-labeled DNA is treated with various chemicals which induce base specific chain breaks with a low frequency. In dideoxy sequencing, or sequencing by the Sanger procedure, a single-stranded DNA is used as a template for synthesis of a labeled complementary strand by a DNA polymerase. Addition of dideoxynucleoside triphosphates will induce base-specific chain termination. In both procedures the nucleotide sequence of the cloned DNA can be deduced after fractionation of the labeled products by polyacrylamide gel electrophoresis. As yet, radioactive labeling of the reaction products is most common, but fluorescence labeling and computer-assisted automated sequence interpretation has become as a powerful alternative during the last years. Further automation of the various processes involved in DNA sequencing will be necessary for the planned sequencing of large genomes, such as the Escherichia coli genome, the yeast genome, and the human genome.