Denaturing polyacrylamide gel electrophoresis.

Polyacrylamide gels that contain a high concentration of urea as a denaturant are capable of resolving short (<500 nucleotides) single-stranded fragments of DNA or RNA that differ in length by as little as one nucleotide. Such gels are commonly used for DNA sequence analysis, as well as in PCR amplification of SSLPs (simple sequence length polymorphisms) for genotyping, genotyping by the ligase chain reaction (LCR), analysis of mutations by RNase A cleavage, chemical cleavage of heteroduplex DNA to identify mutations, and molecular analysis of fragile X syndrome by PCR. This appendix presents a protocol for the pouring, running, and processing of a typical gel which is 40-cm long with a uniform thickness of 0.4 mm, containing 7 M urea and 4% to 8% acrylamide.