The dnaKJ operon in E. coli contains two genes which produce two chaperone and heat shock proteins. Heat shock proteins are induced when cellular stress is present. In addition to heat shock, this stress can also be caused by toxins such as heavy metals in the cell's environment. In this case, the operon is activated by RNA polymerase sigma factor RpoH, also know as sigma 32 or sigma H. This protein is produced when the bacteria is exposed to heat or other stress, and allows other heat shock proteins to be expressed. The first gene in the operon, dnaK, encodes the protein chaperone DnaK, also known as the 70 kilodalton heat shock protein (Hsp70). This chaperone binds to partially synthesized proteins and prevents them from aggregating before folding can occur. It can also bind to proteins that are transported across the cell membrane, as they remain unfolded until they are in place and are at risk for aggregation. When the cell is stressed, proteins can become damaged, leading to unfolding and aggregation. Hsp70 can bind to these proteins, preventing aggregation and allowing proper refolding. The second gene, dnaJ, encodes the protein chaperone DnaJ, which is also known as the 40 kilodalton heat shock protein (Hsp40). This protein also interacts with unfolded protein chains to prevent their aggregation

Operon: DNA Biosynthesis/Heat Shock Protein References