Studies of bacterial genes whose products are involved in heat shock regulation and bacteriophage lambda DNA replication

It was shown previously that the products of the Escherichia coli dnaK and dnaJ genes are required for bacterial growth at high temperatures as well as bacteriophage lambda growth at all temperatures. Both genes encode heat shock proteins; the rate of their expression is increased transiently after a shift to high temperature or after infection by bacteriophage lambda. The DnaK protein is involved in the modulation of the Escherichia coli heat shock response. In this dissertation, it is shown by biochemical analyses, supported by genetic data, that these two proteins interact and are members of a possibly larger protein complex. The product of the dnaJ gene is a 37,000 Mp membrane associated protein, while the product of the dnaK gene is a previously characterized 66,000 Mr, protein. Both proteins were purified. The products of the two genes interact functionally since it is shown that 1) the purified proteins form a complex, consistent with the findings that (a) the two proteins are involved in the same prepriming step of an in vitro bacteriophage lambda DNA replication and, (b) the DnaJ protein, in addition to the DnaK protein, modulates the heat shock response in Escherichia coli. and 2) suppressors of a dnaJ mutation can be isolated which map in the dnaK region of the genome. In an additional study, it is shown that the dnaJ gene product, like that of dnaK. is not absolutely essential for Escherichia coli growth.