大质粒一般指具有传递性功能的质粒,其大小至少在15Mu以上,位于琼脂糖凝胶电泳图谱染色体带的上方,多数为40Mu以上。目前发现的最大质粒为350Mu。大质粒存在于许多种细菌中,构成了宿主菌全部遗传基因不可忽视的一部分。质粒分子量越大,其结构和分子特性就越与染色体相似,应用根据质粒与染色体分子特性不同而设计的分离质粒DNA的方法很难检测出较大质粒。因此,大质粒的检测就成为质粒工作者所面临的新课题。关于细菌质粒的检测方法,我们曾做过较为详细的介绍,本 Large plasmids generally refer to plasmids that have transmissibility and are at least over 15Mu in size and are located above the band of the agarose gel electrophoresis map, most of which are above 40Mu. The largest plasmid currently found is 350Mu. Large plasmids exist in many species of bacteria and constitute a non-negligible part of all host genes in the host bacteria. The larger the molecular weight of a plasmid, the more structurally and molecularly its characteristics are similar to the chromosomes. It is difficult to detect larger plasmids using the method of separating plasmid DNA designed according to the different molecular and chromosomal characteristics of the plasmid. Therefore, the detection of large plasmids has become a new issue facing plasmid workers. About bacterial plasmid detection methods, we have done a more detailed introduction, this