Heat Shock Flashcards
What is the heat shock response?
When a culture of E. coli is subjected to a sudden shift in temperature. Culture is initially grown at about 30 degrees C and then the temp is suddenly increased to 42 degrees C. As a result of this abrupt increase in temp, a triggered response in the bacteria occurs in which there is a rapid increase in production of about 30 different proteins known as “heat shock proteins”.
What are heat shock proteins?
Newly synthesized proteins derived as a result of the abrupt increase in temperature.
What do “heat shock proteins” do?
They are involved in protein folding and stability since many of the regular proteins in the E. coli cell become denatured as a result of the temp increase.
What are some examples of heat shock proteins classified as “chaperones”?
DnaK, Gro E, and Grp E
What is the function of “chaperones”?
Function by binding to a protein as it is being translated and help the protein fold into its final functional conformation. Also help the E. coli cell adapt after a heat shock by binding to denatured proteins and then help the denatured protein fold back into its functional conformation. In other cases the chaperon protein may simply bind to irreversibly denatured proteins and tag them for quick destruction.
What are examples of heat shock proteins that are “proteases” that can degrade badly denatured proteins?
Lon and Clp
What does the gene rpoH code for?
It codes for a sigma subunit of RNA polymerase. However, it does NOT code for the sigma 70 subunit that RNA polymerase uses to recognize and bind to “common” promoter found on most E. coli genes. Instead, it codes for an alternative sigma subunit called “sigma 32”.
What is special about the sigma 32 subunit?
It does not recognize the -35 and -10 sequence code found in common promoters. Instead it recognizes the different sequence found in “heat shock” promoters that lie upstream of most the genes encoding the heat shock proteins.
What is bound to the sigma 32 subunit, keeping it from associating with RNA polymerase?
DnaK
What happens with sigma 32 subunit as there is a sudden shift to higher temp?
DnaK no longer binds to sigma 32 and instead binds to the denatured proteins, therefore allowing sigma 32 subunit to be free to associate with the RNA polymerase and replace the 70 subunit in the holoenzyme. This allows RNA poly to bind to heat shock promoters and initiate transcription.
