The Serratia 39006 Pst transporter is regulated via PhoBR.. A) The Serratia 39006 pstSCAB-phoU genes. (B) Putative Pho boxes found upstream of the pstS, phoB, pigA, smaI and rap genes in Serratia 39006. The E. coli Pho box consensus sequence is shown [10–12]. Conserved nucleotides are shown in bold. (C) β-Glucuronidase activity was assayed throughout growth in LB from a chromosomal pstC::uidA fusion in an otherwise WT background (NW201; diamonds and open bars) or a phoB mutant background (NW202; squares and solid bars). Bars represent β-glucuronidase assays and dashed lines represent bacterial growth.