Multiple cloning site

A multiple cloning site (MCS), also called a polylinker, is a short segment of DNA which contains many (up to ~20) restriction sites—a standard feature of engineered plasmids. Restriction sites within an MCS are typically unique, occurring only once within a given plasmid. The purpose of an MCS in a plasmid is to allow a piece of DNA to be inserted into that region.

MCSs are found in a variety of vectors, including cloning vectors to increase the number of copies of target DNA, and in expression vectors to create a protein product. In expression vectors, the MCS is located downstream of a promoter to enable gene transcription. The MCS is often inserted within a non-essential gene, such as lacZα, facilitating blue-white screening for recombinant selection. By including recognition sequences for a variety of restriction enzymes, the MCS greatly enhances flexibility and efficiency in molecular cloning workflows, allowing for precise DNA insertion in synthetic biology, genetic engineering, and transgenic organism development.