Methods of gene cloning and expression vectors

The techniques of DNA cloning and expression vectors play a vital role in the emerging field of biotechnology. The most significant application of expression vectors is the production of heterologous proteins. Cloning vectors are typically plasmids used to propagate DNA, which replicate in E. coli to high numbers and contain a multiple cloning site (polylinker) with restriction sites suitable for inserting a DNA fragment. In contrast, expression vectors are designed to allow transcription of the cloned gene and its translation into protein. While they share some features with general cloning vectors, such as the multiple cloning sites and a selectable marker, they typically have a lower copy number within cells and lack a screenable marker. Expression vectors also have additional features that enable them to express genes and produce proteins, including a promoter, ribosome binding site, ATG starts codon, a multiple cloning site (polylinker) that ensures inserts are ligated in a predictable reading frame, and often (not always) a fusion tag to aid in purification steps. Therefore, cloning and expression vectors are important tools in recombinant DNA technology. This article reports on the basics of cloning methods and different expression systems in the current context.