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Identification of the Escherichia coli K-12 ybhE Gene as pgl, Encoding 6-Phosphogluconolactonase

Lynn C. Thomason,^1* Donald L. Court,¹ Atin R. Datta,^2, Rita Khanna,^2, and Judah L. Rosner²

Gene Regulation and Chromosome Biology Laboratory, Center for Cancer Research, National Cancer Institute-Frederick, Frederick,¹ Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland²

Received 7 July 2004/ Accepted 7 September 2004

We report identification of the Escherichia coli ybhE gene as the pgl gene that encodes 6-phosphogluconolactonase. A tentative identification was first made based on the known approximate location of the pgl gene and the similarity of the presumptive ybhE-encoded protein sequence to a known Pgl enzyme. To test this notion, the ybhE gene was deleted and replaced with a drug marker. Like previously characterized pgl mutants, the ybhE deletion mutant had a Blu^– phenotype (dark-blue staining with iodine due to accumulation of starch after growth on minimal maltose) and demonstrated impaired growth on minimal glucose medium when combined with a pgi mutation. Biochemical assay of crude extracts for 6-phosphogluconolactonase enzymatic activity showed that ybhE encodes this activity. The ybhE gene was transferred from the E. coli chromosome to an expression vector. This ybhE clone complemented both the precise deletion of the ybhE gene and a larger deletion, pgl8, for the Blu^– phenotype and for phosphogluconolactonase activity, confirming that ybhE is the pgl gene. A newly observed phenotype of pgl strains is a lowered frequency of appearance of Bgl⁺ mutants that can utilize the ß-glucoside salicin. This is likely due to poor growth of Bgl⁺ pgl strains on salicin due to the accumulation of 6-phosphogluconolactone.

Present address: Food and Drug Administration, Rockville, MD 20857.

Present address: International Technology Transfer Management, Inc., Bethesda, MD 20817.

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