GENETIC-BASIS OF THE MBRC PLOIDY PHENOTYPE IN ESCHERICHIA-COLI

The mbrC17 mutation in Escherichia coli had been shown to cause condit ional growth defects and an increase in the quantity of DNA per cell. The present work was aimed at identifying the mutation. Sequencing sho wed that the MbrC17 phenotype does not involve glr (murI), as previous ly suggested. PI transduction data indicated that the mbrC17 mutation is closely linked to rpoB, and allele exchange showed it to lie within the secE-nusG operon. A single change relative to wild type was found in the secE-nusG region from the mbrC17 strain, a G --> A mutation 23 bp upstream of the secE coding sequence. This mutation causes a two-f old increase in the concentration of secE-nusG mRNA.