A NOVEL DNA ELEMENT THAT CONTROLS BACTERIAL HEAT-SHOCK GENE-EXPRESSION

The hspArpoH(1) and hspBCdegP heat shock operons of Bradyrhizobium jap onicum are preceded by a novel, conserved DNA element of approximately 100bp, which is responsible for the temperature-regulated transcripti on of their sigma(70)-type promoters. We designated this motif ROSE fo r repression of heat shock gene expression and found additional ROSE e lements upstream of two newly identified heat shock operons. A critica l core region in the hspA-associated ROSE, was defined by introducing insertions or deletions. While four mutants retained the ability to re press transcription of the hspArpoH(1) operon, five deletion mutants p roduced elevated hspA mRNA levels under low-temperature growth conditi ons. Derepression was confirmed by increased RpoH(1) levels in non-hea t-shocked cells from one of these mutants and by strains that containe d a translational hspA-lacZ fusion associated with mutated ROSE, eleme nts. The hspArpoH(1) operon was efficiently transcribed in vitro, and a deletion of ROSE1 did not impair this activity. Gel retardation expe riments demonstrated that a protein in non-heat-shocked cells specific ally binds to the intact ROSE1 element but not to a mutated element la cking the core region. Taken together, these results indicate that a c entral region of ROSE serves as a binding site for a repressor protein under standard growth conditions in order to prevent the undesired tr anscription of heat shock genes.