Diploidy for a structural gene specifying a major protein of the outer cell envelope membrane from Escherichia coli K-12

Abstract

Homogenotes, heterogenotes and intergeneric hybrids were studied that are diploid for the structural gene of a major outer cell envelope membrane protein (protein II*) from E. coli. This protein can act as a phage receptor. In wild-type homogenotes, diploidy for the gene did not cause a gene dosage effect. It could be shown with 2 heterogenotes that both the chromosomal mutant and the episomal wild-type genes are expressed, and in each case more of the mutant than the wild-type protein species was found in the cell envelope. In no case of 21 phage-resistant mutants missing protein II* was a trans effect observed of the mutant gene on the expression of the episomal wild-type gene. Transfer of E. coli episomes carrying the protein II* structural gene into Salmonella typhimurium and Proteus mirabilis resulted in intergeneric hybrids that became sensitive to the relevant phage and harbored the E. coli protein II* in their cell envelopes. The results may be taken as suggestive evidence for a simple feedback mechanism for the regulation of synthesis of protein II*. There are no highly specific requirements on proten primary structure for incorporation into an outer cell envelope membrane.