Regulation of clpQ(+)Y(+) (hslV(+)U(+)) Gene Expression in Escherichia coli

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 λclpQ(+)::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.