Versatility of *Escherichia coli*

**27**

**Chapter 2**

**Abstract**

inteins

**1. Introduction**

Expression

*and Lai-Cheuk Nelson Lai*

*Escherichia coli*: A Versatile

*Thiyagarajan Sivakumar, Xiu-Hua Hu, Hao Wang* 

*Wan-Keung Raymond Wong, Ka-Lun Ng,* 

promising host choice for heterologous protein expression.

Platform for Recombinant Protein

Among the living organisms, *Escherichia coli* has been the most common choice employed for recombinant protein expression. In addition to its well-characterized genetics, *E. coli* is fast growing, relatively cheap, and easy to handle. These fine properties, in conjunction with the success achieved in transforming plasmid DNA into *E. coli*, as well as the advent of various genetic engineering techniques in the 1970s, have enabled *E. coli* to be considered as the most favorable host for genetic manipulations. The recent advances in better comprehension of regulatory controls of gene expression and the availability of various novel approaches, which include both intracellular, e.g., through intein-mediated expression and self-cleavages, and extracellular, e.g., through the use of secretion signals, to achieve successful expression of the target proteins in *E. coli* further support the view that *E. coli* is the most

**Keywords:** *Escherichia coli*, *E. coli*, recombinant protein expression, heterologous protein, authentic structures, fusion protein, affinity tags, secretion, excretion,

The achievements in unveiling the structure of DNA, deciphering the genetic code, understanding gene expression and regulation, and discovering extrachromosomal DNA (plasmid), restriction endonucleases and DNA ligases in the 1950s and 1960s laid the groundwork for the construction of the first chimeric (recombinant) DNA molecule [1]. In 1973, Cohen and Boyer reported their success in creating the first *Escherichia coli* transformant into which a recombinant plasmid molecule was introduced [2]. The possibility of inserting foreign DNA into *E. coli* has not only allowed the development of a vast number of molecular biology techniques for genetic manipulations, e.g., construction and characterization of cDNA libraries, DNA splicing and amplification, hybridization and sequencing, site-specific mutagenesis, research and applications of bacteriophages and DNA modifying enzymes, studies of regulation of gene expression, etc., but also the exploitation of *E. coli* for use as a surrogate host for the expression of heterologous proteins. Despite the presence of restriction
