The rolA gene is transferred naturally by Agrobacterium rhizogenes to the genome of host plants, where it induces dramatic changes in development of transformed plants, including dwarfism and leaf wrinkling. The predicted translation product of the rolA gene is a small (11.4 kDa), basic (pI = 11.2) protein, which has no clearly significant similarity to sequences in the data bases. We have introduced into the tobacco genome a gene encoding a rolA∷GUS fusion protein. Expression of this gene led to synthesis of an RNA and a protein of expected size, and the transformed plants exhibited the dwarfism and leaf wrinkling typical of rolA plants, but to a lesser degree than plants transformed with the wild-type rolA gene. The distribution of β-glucuronidase (GUS) activity was compared in subcellular fractions of leaf extracts from plants expressing either the rolA∷gus gene or a control gus construct. As expected, in the control plants, GUS activity was essentially cytosolic. In contrast, in plants expressing the rolA∷gus gene the highest specific activity was associated with the plasmalemma fraction.