Gene dosage effects of the structural gene for a lipoprotein of the Escherichia coli outer membrane

The gene dosage effects of the structural gene (lpp) for the lipoprotein of the E. coli outer membrane were examined. A novel F-prime factor containing the lpp gene was constructed. The amount of the free-form lipoprotein in the merodiploid strain carrying the F-prime factor was found to be about two times as great as that in the corresponding haploid strain. On the other hand, the amount of the bound-form lipoprotein, which is covalently linked to the peptidoglycan, was not significantly different in the merodiploid strain as compared with the corresponding haploid strain. The present results suggest that the lpp gene is expressed constitutively in contrast to another major protein of the E. coli outer membrane, tolG protein (protein II*). The F-prime factor isolated may include a portion of the E. coli chromosome (located between 33 and 36 min on the genetic map) that is not covered by any other F-prime factor.