ChainTerminationMethode

ChainTerminationMethode is a DNA sequencing method used to determine the order of nucleotides in a DNA molecule. It relies on controlled DNA synthesis in which chain termination events mark the end of growing strands, allowing the construction of a set of fragments that encode the sequence information.

The principle centers on incorporating chain-terminating nucleotides, known as dideoxynucleotides (ddNTPs), which lack the 3' hydroxyl group required for further extension. During polymerase-catalyzed replication, the occasional incorporation of a ddNTP terminates the chain. Four separate reactions or a single labeled reaction set contain all four normal nucleotides and a small proportion of ddNTPs corresponding to adenine, thymine, cytosine, and guanine. The resulting fragments differ in length, terminating at each occurrence of the respective base.

Historically, four reactions were run in parallel and the terminated fragments were separated by polyacrylamide or agarose gel electrophoresis to reveal the sequence. Modern implementations commonly use fluorescently labeled ddNTPs and capillary electrophoresis, enabling the entire sequence to be read in a single lane by detecting the color of each terminated fragment. The method produces high accuracy over readable lengths and is capable of generating reliable sequences up to about one thousand bases in capillary systems.

ChainTerminationMethode played a pivotal role in early DNA sequencing and remains a foundational reference in molecular biology. It is widely used for small-scale sequencing tasks, plasmid verification, and educational purposes, though next-generation sequencing technologies now dominate large-scale genomics projects.