Detection of Circular Plasmid DNA by MultiNA™

Introduction

Various plasmids are used in gene recombination experiments, and in recent years, plasmids have also been used in storage and distribution of bioresources due to their convenience. Conventionally, agarose gel electrophoresis has been used to measure the purity and size of plasmids, but plasmids can exist in conformations with different 3-dimensional structures, even in the same nucleotide sequence, and this affects the mobility of plasmids when passed through a molecular sieve in electrophoresis. The different 3-dimensional structures are the three conformations called supercoiled, open-circular, and linear, as illustrated in Fig. 1. The supercoiled conformation contains no nicks in the double-stranded DNA and has a shape like a tightly-twisted rubber band. The open-circular conformation has a circular shape in which the twisting is relaxed (i.e., the supercoils are released) by a nick in one strand of the double-stranded DNA. The linear type is a straight chainlike conformation resulting from complete cutting of both strands in any part of the double-stranded DNA. Since these three conformations have different apparent sizes, the sizes of plasmids detected by agarose gel electrophoresis may differ, depending on the three conformations, even when the size of plasmids is identical. At present, microchip electrophoresis (MCE) systems have gained wide acceptance as an alternative technique to conventional agarose gel electrophoresis. Among these systems, the Shimadzu MCE-202 MultiNA microchip electrophoresis system can perform all of the work processes of agarose gel electrophoresis automatically. This article introduces an actual example of an analysis of three types of plasmids using the MultiNA microchip electrophoresis system and an agarose gel electrophoresis system.

December 10, 2020 GMT