Unexpected Presence of Defective glpR Alleles in Various Strains of Escherichia coli

Alleles of glpR associated with the same GlpR(−) phenotype produce substitutions in different conserved portions of the glycerol 3-phosphate repressor which are not part of the helix-turn-helix motif. Analysis of the effects on growth and enzyme expression show that glucose repression of glycerol utilization is not dependent on a functional repressor.