MadSci Network: Molecular Biology

Re: Why is DNA end-labelled before sequencing?

Date: Wed Dec 10 20:29:14 2003
Posted By: Dmitri Leonoudakis, Post graduate researcher
Area of science: Molecular Biology
ID: 1067622019.Mb

Sequnced DNA is end labled with dideoxynucleotide with a radioactive 
phosphate.  When the labeled DNA is separated by polyacrylamide gel 
electrophoresis, the sequencing products are separated based on their 
size.  Products which have terminated short will run faster in the gel. 
Following separation the pruducts all need to be uniformly labeled to give 
a banding pattern of even intensity.  Each product will only be labeled 
once at its end, therefore each product should be able to be visualized 
equally.  The incorporated radioactive nucleotides enable the DNA to be 
visualized using X-ray film which is very sensitive.

Sambrook, Fritcsh, and Maniatis, Molecular Cloning, A Laboratory Manual, 
1989, page 13.5-13.7

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