载体操作中最常用的几个概念：

1. The lac Z gene may be used as a simple "reporter" gene, separated from its natural promoter. For example, we might put the lac Z gene in front of a mammalian promoter, transfect the DNA into mammalian cells, and then fix and stain a tissue with X-gal. The cells that turn blue must have the beta galactosidase enzyme, the product of the lac Z gene, which could only have been expressed from the donated promoter. Ergo - the promoter was active. Actually, there are controls that are needed to make this brave statement, but you get the idea. We used only the coding sequence for the bacterial enzyme as a reporter, and it has nothing to do with the lac promoter in this scenario.

2. We may use the lac promoter to drive or regulate expression of any gene in an appropriate prokaryotic cell (e.g. E. coli, where it comes from). That is, lac Z may be nowhere in the picture. We've just taken the regulatory machinery and are using it without the downstream genes.