ABSTRACT
Obtaining pure protein samples is a critical first step for many experiments. While a small number of highly abundant proteins can be purified directly from natural sources, most interesting proteins must be obtained by heterologous expressions or total chemical synthesis. The first step in the heterologous expression and purification of proteins is choosing an appropriate expression system. Bacterial expression systems are some of the most common heterologous expression systems employed. These are the easiest expression systems to use and have the advantage of producing extremely large quantities of protein. There are a number of different ways to obtain a gene of interest. If the protein has been previously studied, it may be possible to obtain the genetic material from another research group. There are two main classes of promoters used for protein expression: constitutively active promoters and inducible promoters. Typically, protein expression vectors include tags for purification and immunohistological identification of the heterologously expressed protein.
