Environmental control of invasin expression in Yersinia pseudotuberculosisis mediated by regulation of RovA, a transcriptional activator of the SlyA/Hor family

Invasin is the primary invasive factor of Yersinia pseudotuberculosis that allows efficient internalization into eukaryotic cells. We investigated inv asin expression and found that the inv gene is regulated in response to a v ariety of environmental signals, such as temperature, growth phase, nutrien ts, osmolarity and pH, and requires the product of rovA, a member of the Sl yA/Hor transcriptional activator family. The rovA gene was found by a genet ic complementation strategy that restores temperature regulation of an unex pressed inv-phoA fusion in Escherichia coli K-12. RovA plays a role in the invasion of Y. pseudotuberculosis into mammalian cells and mediates the reg ulation of invasin in response to all environmental signals analysed. Delet ion analysis of the inv promoter region revealed a DNA segment extending 20 7 bp upstream of the transcriptional start site, which is required for maxi mal RovA-Induced inv transcription. Gel retardation assays showed that RovA interacts preferentially with this promoter fragment and suggested two pot ential RovA binding sites. Studies with chromosomal gene fusions also demon strated that rovA follows the same pattern of regulation as invasin, indica ting that environmental control of inv expression is mainly mediated by the control of RovA synthesis, Furthermore, we showed that a rovA-lacZ fusion is only slightly expressed in a rovA mutant strain, indicating that a posit ive autoregulatory mechanism is also involved in rovA expression.