The use of transposon Tn phoA to detect genes for cell envelope proteins subject to a common regulatory stimulus : Analysis of osmotically regulated genes in Escherichia coli

Abstract

The transposon Tn phoA can be used specifically to detect bacterial genes that code for cell envelope proteins. We have used Tn phoA to search for genes regulated by osmolarity in Escherichia coli. Among approximately 30,000 random insertions of Tn phoA into the chromosome, we have found 700 independent fusions that produce hybrid proteins with alkaline phosphatase activity. Of these, 37 were induced after growth in a medium of high osmolarity and none was repressed. Osmo-inducible fusions of phoA were found to ompC and to a gene that is probably proU. These two genes were already known to be transcriptionally induced by osmolarity. In addition, eight other genes, designated osm, were identified and mapped on the bacterial chromosome. The expression of these genes is induced by solutes that are unable to decrease the turgor pressure applied to the envelope. One of the osm genes, osmI, is also specifically induced by glycerol, which does diffuse across the cytoplasmic membrane. The expression and osmoregulation of all the osm genes were shown to occur independently of ompR and envZ, which control the expression and osmoregulation of the ompC and ompF genes in E. coli.