Escherichia coli gene ydeA encodes a major facilitator pump which exports L-arabinose and isopropyl-beta-D-thiogalactopyranoside

Abstract

Inactivation of the Escherichia coli gene ydeA, which encodes a member of the major facilitator superfamily, decreased the efflux of L-arabinose, thereby affecting the expression of AraC-regulated genes. In addition, overexpression of ydeA decreased the expression of genes regulated by isopropyl-beta-D-thiogalactopyranoside.

FIG. 1

Map of the chromosomal region carried by suppressing plasmids and location of mini-tet insertions. Gene b numbers (1a) are indicated below four-letter designations (18). Relevant putative promoters are shown above intergenic spaces. Mini-tet insertions in ydeA are indicated by vertical arrows. The size of the pMESBA24 insert is 7,460 bp.

FIG. 2

Arabinose efflux in ydeA⁺ and ydeA::mini-tet strains. Strains JS219 (ydeA⁺) and JS1910 (ydeA::mini-tet) were grown in M9 medium supplemented with 1 μg of thiamine/ml, 0.2% Casamino Acids, and 1% glycerol until the OD₆₀₀ was nearly 0.6. Cultures (5 ml) were transferred to 25°C, and ³H-labeled l-Ara (5 μM [0.2 Ci/mmol]; Moravek Radiochemicals) was added for 15 min. The cells were filtered through a 48-mm-diameter 0.45-μm HAWP Millipore filter and washed briefly with and resuspended into the same volume of Ara-free medium. Then, 0.2-ml samples were taken at 1-min (JS219) or 2-min (JS1910) intervals, filtered through 25-mm-diameter Millipore filters, washed, and counted. Open squares, JS219; closed squares, JS1910.