Molecular analysis of the glpFKX regions of Escherichia coli and Shigella flexneri.

We have identified a new gene, glpX, belonging to the glp regulon of Escherichia coli, located directly downstream of the glpK gene. The transcription of glpX is inducible with glycerol and sn-glycerol-3-phosphate and is constitutive in a glpR mutant. glpX is the third gene in the glpFKX operon. The function of GlpX remains unknown. GlpX has an apparent molecular weight of 40,000 on sodium dodecyl sulfate-polyacrylamide gels. In addition to determining the E. coli glpX sequence, we also sequenced the corresponding glpFKX region originating from Shigella flexneri, which after transfer into E. coli was instrumental in elucidating the function of glpF in glycerol transport (D. P. Richey and E. C. C. Lin, J. Bacteriol. 112:784-790, 1972). Sequencing of the glpFKX region of this hybrid strain revealed an amber mutation instead of the tryptophan 215 codon in glpF. The most striking difference between the E. coli and S. flexneri DNA was found directly behind glpK, where two repetitive (REP) sequences were present in S. flexneri, but not in the E. coli sequence. The presence or absence of these REP sequences had no effect on transport or on growth on glycerol. Not including the REP sequence-containing region, only 1.1% of a total of 2,167 bp sequenced was different in the two sequences. Comparison of the sequence with those in the EMBL data library revealed a 99% identity between the last third of glpX and the first part of a gene called mvrA. We show that the cloned mvrA gene (M. Morimyo, J. Bacteriol. 170:2136-2142, 1988) originated from the 88-min region of the Escherichia coli chromosome and not, as reported, from the 7-min region and that the gene product identified as MvrA is in fact encoded by a gene distal to glpX.