ROSE elements occur in disparate rhizobia and are functionally interchangeable between species

Expression of at least ten genes in Bradyriazobium japonicum, seven of whic h code for small heat shock proteins (sHsps), is under the control of ROSE (repression of heat shock gene expression). This negatively cis-acting DNA element confers temperature control to a (:FO-type promoter. Here, we show that ROSE elements are not restricted to B. japonicum but are also present in Bradyrhizobium sp. (Parasponia.), Rhizobium sp. strain NGR234 and Mesorh izobium loti. Am overall alignment of all ROSE sequences reveals a highly c onserved and probably functionally important region towards the 3'-end of t he element. Moreover, we provide genetic evidence for the previously propos ed presence of multiple sHsps in these organisms. Primer-extension data of five newly identified ROSE-associated operons show that transcription is re pressed at low temperatures and induced after a temperature upshift. Transl ational ROSE-hsp'-'lacZ fusions of Bradyrhizobium sp. (Parasponia) and Rhiz obium sp. strain NGR234 integrated into the chromosome of B. japonicum were heat-responsive. The functionality of these heterologous ROSE elements hin ts at a common regulatory principle conserved in various rhizobia.