ABSTRACT
The immune system of bacteria against phage shares a lot of similarity with that of mammals, especially the adaptive immune system.The elements and components of the bacterial adaptive immune system———clustered regularly interspaced short palindromic repeats ( CRISPR ) and the mammalian adaptive immune system have a lot of parallel mechanisms.We could acquire new understanding about the immune function of CRISPR systems through that analogy.In recent years, researchers have found CRISPR-Cas system can play significant roles in regulating bacterial growth and metabolism.These researches have revealed new functions of CRISPR beyond immunity.The ability of CRISPR to affect gene expression has attracted increasing attention.Further studies are needed to shed light on the complicated functions of CRISPR.