FIG. 1.

(A and B) Western blot analyses of GroEL and DnaK in C. crescentus strains containing different levels of ς³². NA1000 cells carrying (A) or not carrying (B) plasmid pAR33 (high-copy-number plasmid containing the C. crescentus rpoH gene) were grown to mid-log phase at 30°C or shifted to 42°C for the indicated times (minutes). Protein extracts were prepared and separated by SDS-polyacrylamide gel electrophoresis. The proteins were transferred to nitrocellulose membranes and probed with antibody to C. crescentus GroEL or C. crescentus DnaK and antibody against E. coli ς³², as described in Materials and Methods. Bound antigen was visualized by chemiluminescence and recorded on X-ray film. Equal amounts of protein were applied to each lane. (C) The relative levels of ς³², GroEL, and DnaK, determined by densitometry scanning of the films, for strains NA1000 (○) and NA1000 carrying pAR33 (▪) are shown.