When cells of the cyanobacterium Synechocystis sp. PCC 6803 are exposed to high temperature they perceive changes in the growth conditions and regulate the expression of genes and synthesize heat-inducible proteins as a response to the heat stress. DNA microarray analysis revealed that genes for chaperonins and proteases, such as groESL1, groEL2, htpG, hspA, and clpB1 were transiently induced after incubation of the cells at 44 degrees C for 20 min. Quantitative two-dimensional gel electrophoresis revealed that the levels of these chaperonins and proteases were elevated after incubation of cells at 44 degrees C for 60 min. These findings indicated that levels of the mRNAs and proteins of chaperonins were well correlated in the cells of Synechocystis. However, the level of elongation factors are mainly regulated at the protein level. These results indicated that acclimation to the heat-shock conditions might be governed by transcriptional and translational regulation in Synechocystis.