ClpB is the Escherichia coli heat shock protein F84.1.
ClpB is thought to be involved in proteolysis because of its sequence similarity to the ClpA subunit of the ClpA-ClpP protease. It has recently been shown that ClpP is a heat shock protein. Here we show that ClpB is the Escherichia coli heat shock protein F84.1. The F84.1 protein was overproduced in strains containing the clpB gene on a plasmid and was absent from two-dimensional gels from a clpB null mutation. Besides possessing a slower growth rate at 44 degrees C, the null mutant strain had a higher rate of death at 50 degrees C. We used reverse transcription of in vivo mRNA to show that the clpB gene was expressed from a sigma 32-specific promoter consensus sequence at both 37 and 42 degrees C. We noted that the clpB+ gene also caused the appearance of a second protein spot, F68.5, on two-dimensional gels. This spot was approximately 147 amino acids smaller than F84.1 and most probably is the result of a second translational start on the clpB mRNA. F68.5 can be observed on many published two-dimensional gels of heat-induced E. coli proteins, but the original catalog of 17 heat shock proteins did not include this spot.
Squires
C L
CL
Department of Biological Sciences, Columbia University, New York, New York 10027.
Pedersen
S
S
Ross
B M
BM
Squires
C
C
D001483:Base Sequence; D049071:Endopeptidase Clp; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005838:Genotype; D006360:Heat-Shock Proteins / Q000235:genetics*; D006358:Hot Temperature; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D015345:Oligonucleotide Probes; D010957:Plasmids; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid
D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D015345:Oligonucleotide Probes; D049071:Endopeptidase Clp; C069775:ClpB protein, E coli