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.

An MCS is 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 the promoter.