The Escherichia coli ClpYQ (HslUV) complex is an ATP-dependent protease, and the clpQ⁺Y⁺ (hslV⁺U⁺) operon encodes two heat shock proteins, ClpQ and ClpY, respectively. The transcriptional (op) or translational (pr) clpQ⁺::lacZ fusion gene was constructed, with the clpQ⁺Y⁺ promoter fused to a lacZ reporter gene. The clpQ⁺::lacZ (op or pr) fusion gene was each crossed into lambda phage. The λlpQ⁺::lacZ⁺ (op), a transcriptional fusion gene, was used to form lysogens in the wild-type, rpoH or/and rpoS mutants. Upon shifting the temperature up from 30 ° C to 42 ° C, the wild-type λclpQ⁺::lacZ⁺ (op) demonstrates an increased β-galactosidase (βGal) activity. However, the βGal activity of clpQ⁺::lacZ⁺ (op) was decreased in the rpoH and rpoH rpoS mutants but not in the rpoS mutant. The levels of clpQ⁺::lacZ⁺ mRNA transcripts correlated well to their βGal activity. Similarly, the expression of the clpQ⁺::lacZ⁺ gene fusion was nearly identical to the clpQ⁺Y⁺ transcript under the in vivo condition. The clpQ(m1)::lacZ⁺, containing a point mutation in the -10 promoter region for RpoH binding, showed decreased βGal activity, independent of activation by RpoH. We conclude that RpoH itself regulates clpQ⁺Y⁺ gene expression. In addition, the clpQ⁺Y⁺ message carries a conserved 71 bp at the 5' untranslated region (5'UTR) that is predicted to form the stem-loop structure by analysis of its RNA secondary structure. The clpQ(m2)Δ40::lacZ⁺, with a 40 bp deletion in the 5'UTR, showed a decreased βGal activity. In addition, from our results, it is suggested that this stem-loop structure is necessary for the stability of the clpQ⁺Y⁺ message.