There are multiple cloning and expression vectors (plasmids) and different expression promotors available for E. coli, which makes it useful as a host for recombinant protein expression.
E. coli has a high growth rate, can reach a high cell density, and generally has a high recombinant expression level. However, E. coli is not good at protein secretion (into the periplasmic space) or excretion (release into the medium), which makes it less suitable as a host for recombinant expression of extracellular proteins containing disulfide bridges. Recombinant protein expression in E. coli may lead to protein misfolding and formation of inclusion bodies.
However, misfolded recombinant protein from inclusion bodies can be purified and sometimes refolded into active recombinant protein. E. coli is unable to make a number of post-translational modifications including simple and complex protein glycosylation found in eukaryotes.