Heat-shocked S30 extract (HS-S30 extract) was prepared from cells of Escherichia coli strain Q13 exposed to elevated temperatures (from 37 degrees C to 42 degrees C) for 30 min. In a cell-free system with HS-S30 extract, the synthesized CAT protein had higher specific activity than that synthesized by a cell-free system with S30 extract prepared from Q13 cells incubated at 37 degrees C. SDS-PAGE analysis showed that the heat-shock proteins, GroEL and DnaK, which are known to be molecular chaperones, were significantly increased in the HS-S30 extract. The addition of GroEL or DnaK to the S30 extract system increased the specific activity of the synthesized CAT protein. Heat-shock induction thus offers an effective method of modifying E. coli cell extracts.