H-088. Role of C1-Hydroxyl Configuration of D-Galactose in Modulation of Gal Repressor Activity

S. Lee, D. E. A. Lewis, S. Adhya;
NCI, NIH, Bethesda, MD.

The galactose operon constitutes metabolic enzymes (GalETKM) of which GalK, GalT, and GalE convert D-galactose to a D-glucosyl moiety in E. coli. The galactose mutarotase (GalM) catalyzes the interconversion between β-D-galactose and α-D-galactose. Both β-D-galactose and α-D-galactose are natural metabolites and critical components in cell. Although the galactose operon is induced by D-galactose, it has not been clear whether α- and/or β-anomers induce the gal operon. In vitro transcription assays with pure α- and β-D-galactoses showed that both anomers are active as inducers. However, the methylation of α-D-galactose, unlike that of β-D-galactose, could not induce the gal promoters. We also tested other D-galactose analogues and derivatives for inducibility in gal transcription in vitro. Our results suggest that modification of the C1-hydroxyl group when in α-, and not in β-configuration in D-galactose inactivates the effect of the sugar on GalR in transcription derepression.