Recent studies on the cellular synthesis of various glucosides have taught us that in contrast to the catabolism of glucose the anabolic processes require the mediation of uridine diphosphoglucose (UDPG) T or related nucleotides. 1 2 The biosynthesis of the anabolic mediator, UDPG, proceeds via UTP and G-1-P by means of a specific enzyme UDPG pyrophosphorylase.3' 4 We shall use the term UDPG synthetase instead of UDPG pyrophosphorylase in order to be more explicit about the problem with which we are dealing in this paper, i.e., cellular synthesis of UDPG and of polyglucoside compounds. In the course of our studies on mutants of E. coli K-12, we have encountered a mutant, Gal 23,5a, which by the token of microbiological assays on EMB galactose agar would be classified as a "galactose-negative" mutant. It was found to have only very low capacity to incorporate galactose into insoluble carbohydrate compounds. When cells of Gal 23 were grown on ammonia mineral medium with glycerol as a carbon source, addition of galactose to the medium induced a cessation of growth comparable to that seen in transferaseless mutants.6 Surprisingly enough, enzymatic assays of the enzymes of galactose metabolism' revealed that this galactose-negative and galactose-sensitive strain contained all three enzymes, i.e., K, T, and E. All these observations focused our attention toward a genetic block in the pathway of synthesis of UDPG, especially the enzyme UDPG synthetase. This hypothesis has been fully substantiated as will appear from the present study. Meantime Fukasawa et al.5 described two mutants of E. coli K-12 which they found to be defective in UDPG synthetase. They also reported that these mutants contain no detectable amount of hexose in their cell walls, and that their major cellwall components are heptoses and hexosamines. These observations will be discussed in conjunction with our own findings.

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