Genetic mapping of regulator gene phoS for alkaline phosphatase in Escherichia coli.

Synthesis of alkaline phosphatase in Escherichia coli is repressed in the presence of a high concentration of orthophosphate in a medium. Formation of the enzyme is under a control of two regulator genes, phoR and phoS, and mutation in either phoR or phoS overcomes a repression produced by the presence of a high concentration of orthophosphate. The phoR gene lies close to a structural gene of alkaline phosphatase (phoA), and the phoS gene is located between the genes controlling the synthesis of arginine and isoleucine-valine (H. Echols et al., J. Mol. Biol. 3:425, 1961; A. L. Taylor and M. S. Thoman, Genetics 50:659, 1964). However, the proposed location of the phoS gene does not agree with the fact that it is not present on episome F'14, which carries several loci governing the synthesis of arginine, methionine, and isoleucine-valine (A. J. Pittard, personal communication). Therefore, an experiment was carried out to determine more accurately the location of the phoS gene on the E. coli chromosome (Table 1). Since the phoS gene was shown to be located close to the methionine gene, it was assumed that the phoS gene might be jointly transducible by phage Plkc with markers located near to the methionine gene. To test this possibility, Plkc prepared in an ilv+ metE+ phoSstrain was used to transduce phoSinto an ilvmetEphoS+ recipient, and selection was made for transductants receiving ilv+ or metE+ singly or for those receiving both ilv+ and metE+. When metE+ donor marker was selected, 253 of 300 (84%) metE+ transductants carried the unselected donor marker ilv+, but none received the phoSgene. However, when selected for ilv+, about 30% of the ilv+ transductants carried the unselected donor marker phoS-. Of 116 transductants receiving ilv+ phoS-, no metE+ was obtained. When selected for ilv+ metE+, none received phoS(Table 2). The results suggest that the order of the gene is phoS-ilv-metE. When phage lysates prepared on C90 or C75b