Protease Do is essential for survival of Escherichia coli at high temperatures: its identity with the htrA gene product.

The DNA encoding protease Do was isolated from an E. coli genomic DNA library in lambda gt11, and cloned into a Bluescript plasmid. The cells transformed with the recombinant plasmid were able to overproduce protease Do and grew normally. A mutant lacking the protease activity was also isolated by interrupting the chromosomal DNA with the kan gene. The mutant showed a prolonged lag period and reduced ability to degrade cell proteins as compared to its wild type. Moreover, they were unable to survive at high temperatures, similarly to the htrA mutants. These results suggest that protease Do may play an important role in the intracellular protein breakdown and is essential for survival at high temperatures. Identity of protease Do with the htrA gene product is discussed.