Positive regulator partially required for expression of genes in the locus of effacement (LEE) large pathogenicity island (PAI). Also partially responsible for expression of neighboring gene dlsT (yhaO) during late exponential growth. Binds to DNA of promoter 1 in LEE and DNA from the dlsT promoter region. Induced under conditions that maximally induce expression of the locus of effacement (LEE) large pathogenicity island (PAI). Not induced by D-serine. Decreased expression genes in LEE and of neighboring gene dlsT. Decreased secretion of a number of substrates for type III secretion system (TTSS) encoded in the locus of effacement (LEE) including Tir, EspA and EspD; at least EspD is also decreased intracellularly. Expression of 103 genes is altered; down-regulation of LEE PAI (including the TTSS) plus other genes as well as up-regulation of 29 genes. Decreased ability to form attachment/effacing lesions on HeLa cells; those which form attachments condense host actin less well (pedestal formation) (PubMed:26727373). Belongs to the LysR transcriptional regulatory family.