Pulsed-field electrophoresis of megabase-sized DNA.

Success in constructing a physical map of the human genome will depend on two capabilities: rapid resolution of very large DNA and identification of migration anomalies. To address these issues, a systematic exploration of pulsed-field electrophoresis conditions for separating multimegabase-sized DNA was undertaken. Conditions were found for first liberating and then separating DNA up to 6 megabases at higher field strengths and more rapidly than previously reported. In addition, some conditions for transversely pulsed fields produced mobility inversion, in which increased size was accompanied by faster rather than slower migration. Importantly, anomalous migration could be identified by the presence of lateral band spreading, in which the DNA band remained sharply defined but spread laterally while moving down the gel. These results have implications for both practical applications and theoretical models of pulsed-field electrophoresis.