Nucleotide sequence of the Erwinia chrysanthemi gene encoding 2-keto-3-deoxygluconate permease

Abstract

The phytopathogenic bacterium Erwinia chrysanthemi produces a group of pectolytic enzymes able to depolymerise the pectic compounds in plant cell walls. The resulting tissue maceration is known as soft rot disease. The degraded pectin products are transported by 2-keto-3-deoxygluconate permease into the bacterial cell, where they serve as carbon and energy sources. This H+ coupled transport system is encoded by the kdgT gene; we report the nucleotide sequence of kdgT. It is encoded by an open reading frame (ORF) of 1194 bp, which is preceded by an Escherichia coli-type promoter region. The ORF encodes a protein with 398 amino acid (aa) residues and a predicted Mr of 48,550. As would be expected for a membrane protein, it is very hydrophobic, containing 63% nonpolar aa. However, the kdgT gene has no apparent evolutionary relationship to other genes encoding sugar transport proteins, such as lacY, melB or the E. coli citrate transport gene. Southern hybridization experiments indicate a strong homology between the Er. chrysanthemi and E. coli kdgT genes; there is also a second region on the E. coli chromosome with homology to kdgT. The kdgT gene is located near the ade-377 marker on the Er. chrysanthemi chromosome (equivalent to the region between 20 and 30 min in E. coli), whereas the E. coli kdgT gene is located at 88 min. Thus, these two enterobacteria show some significant differences in their genomic organization.