Positive regulator for the plasmid-encoded virulence factors SpvA, SpvB, and SpvC. A disruption of this gene is no longer virulent in mouse infection. 20-fold reduction in cytopathic effects in human monocyte-derived macrophages, loss of actin depolymerization in macrophages. In Salmonella spp. the spv gene cluster is encoded on a highly transmissible plasmid. Belongs to the LysR transcriptional regulatory family.