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We have identified the grpE gene product as the B25.3 heat shock protein of Escherichia coli on the following evidence: (i) a protein similar in size and isoelectric point to B25.3 was induced after infection of UV-irradiated bacteria by A grpE+ transducing phage, (ii) mutant phage A grpE40, isolated by its inability to propagate on grpE280 bacteria, failed to induce the synthesis of the B25.3 protein, and (iii) A grpE+ revertants, derived from phage grpE40 as able to propagate on grpE28O bacteria, simultaneously recovered the ability to induce synthesis of the B25.3 protein. In addition, we show that E. coli bacteria carrying the grpE280 mutation are temperature sensitive for bacterial growth at 43.5°C. Through transductional analysis and temperature reversion experiments, it was demonstrated that the grpE280 mutation is responsible for both the inability of k to replicate at any temperature tested and the lack of colony formation at high temperature. At the nonpermissive temperature the rates of synthesis of DNA and RNA were reduced in grpE280 bacteria.

After being subjected to a sudden rise in temperature, all organisms tested, from Escherichia coli to Homo sapiens, induce the synthesis of a group of so-called heat shock (HS) proteins, some of which are highly conserved among species (for reviews, see references 9, 21, and 25). A number of laboratories have begun to investigate the properties of these proteins and their expression. Regulation of the HS response is understood in part. In E. coli, induction of the HS response occurs at the transcriptional level under the control of the rpoH gene product, a32. The c32 polypeptide allows RNA polymerase enzyme to specifically recognize HS promoters which have a consensus sequence distinct from that recognized by the normal sigma factor, ac70, encoded by rpoD (8,15). One of the negative regulators of the HS response is the DnaK HS protein (30). This 70-kilodalton protein shows approximately 50% amino acid identity with the Hsp7O family of proteins present in all cells examined (4, 9, 21). DnaK and its eucaryotic homologs appear to mediate protein stabilization, refolding, and dissociation (6,19,26). As an example, during initiation of A DNA replication, the DnaK and DnaJ HS proteins, which are essential for A DNA replication, catalyze the ATP-dependent dissociation of A P protein from a complex which includes the X 0, A P, and E. coli DnaB proteins assembled at oriA (20). The A P protein binds to DnaB and inhibits its helicase activity, which is absolutely necessary for the initiation of A DNA replication (20).The E.

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