Journal of Bacteriology, October 1998, p. 5165-5172, Vol. 180, No. 19
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
andDepartment of Chemical Engineering, University of Washington, Seattle, Washington 98195
Received 24 April 1998/Accepted 30 July 1998
We have constructed an Escherichia coli strain lacking
the small heat shock proteins IbpA and IbpB and compared its growth and
viability at high temperatures to those of isogenic cells containing
null mutations in the clpA, clpB, or
htpG gene. All mutants exhibited growth defects at 46°C,
but not at lower temperatures. However, the clpA,
htpG, and ibp null mutations did not reduce cell viability at 50°C. When cultures were allowed to recover from
transient exposure to 50°C, all mutations except
ibp
led to suboptimal growth as the recovery temperature was raised.
Deletion of the heat shock genes clpB and htpG
resulted in growth defects at 42°C when combined with the
dnaK756 or groES30 alleles, while the
ibp mutation had a detrimental effect only on the growth of dnaK756 mutants. Neither the overexpression of these
heat shock proteins nor that of ClpA could restore the growth of
dnaK756 or groES30 cells at high temperatures.
Whereas increased levels of host protein aggregation were observed in
dnaK756 and groES30 mutants at 46°C compared
to wild-type cells, none of the null mutations had a similar effect.
These results show that the highly conserved E. coli small
heat shock proteins are dispensable and that their deletion results in
only modest effects on growth and viability at high temperatures. Our
data also suggest that ClpB, HtpG, and IbpA and -B cooperate with the
major E. coli chaperone systems in vivo.
Present address: Department of Chemical Engineering, University of
Texas, Austin, TX 78712.
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