Activation by gene amplification of pitB, encoding a third phosphate transporter of Escherichia coli K-12.

Two systems for the uptake of inorganic phosphate (P(i)) in Escherichia coli, PitA and Pst, have been described. A revertant of a pitA pstS double mutant that could grow on P(i) was isolated. We demonstrate that the expression of a new P(i) transporter, PitB, is activated in this strain by a gene amplification event.