It's a gene that's on the plasmid, and this particular gene confers a specific biological property to cells that have the plasmid and can use it properly.

它是质粒自带的基因,如果细胞能够获得这种质粒,并正确的利用它的话,这段基因就能赋予该细胞某种生物学特性

耶鲁公开课 - 生物医学工程探索课程节选