Ultrasensitive plasmid mapping by high performance capillary electrophoresis

This paper compares high performance capillary electrophoresis (HPCE) and conventional slab electrophoresis in mapping of four closely related plasmids with three different restriction enzymes. The plasmids express full length and truncated forms of a growth factor receptor oncogene product and were digested with Hpa II, Hae III and Rsa I. The resulting oligonucleotide fragments were under 2000 base pairs in length, a size well suited to separation by HPCE with linearpolyacrylamide as a sieving matrix. Plasmid mapping is an essential tool in biotechnology both for the design of an expression system and for monitoring the stability of the expression system during fermentation. HPCE can yield much higher resolution of oligonucleotides than attainable in conventional agarose gel electrophoretic procedures for plasmid mapping. In the examples described here, the Hpa II digests provided the surest identification of individual plasmids in the HPCE analysis and could discriminate among all four plasmids. In conventional slab electrophoresis, however, the Rsa I digests provided the best discrimination, although two of the plasmids in this system yielded essentially identical electrophoretic patterns. Hence the optimal restriction enzyme for plasmid mapping applications with HPCE may differ from that selected on the basis of conventional slab gel analysis, and the former technique can provide higher discrimination among related plasmids. The advantages of the HPCE format with respect to speed, low sample consumption and resolution are described.