The spliceosomal intron of rolA gene of Agrobacterium rhizogenes is a prokaryotic promoter.

Agrobacterium rhizogenes transfers DNA (T-DNA)from its Ri plasmid to plant cells. All T-DNA genesare expressed in plant cells. The rolA gene is the onlyT-DNA gene that contains an intron in the untranslatedleader region of its mRNA. This paper showsthat (i) the rolA gene is also transcribed in bacteria;(ii) the 85 bp corresponding to the spliceosomalintron drives prokaryotic gene expression in agrobacteria,in free-living rhizobia and in bacteroidswithin root nodules; and (iii) promoter activity isabolished by the deletion of 63 bp from its 50 end andis reduced by mutations changing its sequence nearthe putative 210 region. The expression pattern of achimeric reporter gene shows that, in free-livingbacteria, gene expression takes place during theexponential phase of growth and increases at theonset of the stationary phase. Within root nodules,reporter gene expression occurs in the invasion,nitrogen fixing and senescent zones.