<jats:p> Uridine diphosphate (UDP)-glucose dehydrogenase, the enzyme that converts UDP-glucose to UDP-glucuronic acid, was derepressed in a mucoid ( <jats:italic>capR9</jats:italic> ) strain of <jats:italic>Escherichia coli</jats:italic> K-12 and repressed in a nonmucoid ( <jats:italic>capR</jats:italic> <jats:sup>+</jats:sup> ) strain. A nonmucoid mutant (strain MC 152; <jats:italic>capR9 non-2</jats:italic> ) derived from the mucoid strain accumulated large quantities of nucleotides. Among these nucleotides, UDP-glucuronic acid was identified as well as guanosine triphosphate and an adenosine diphosphate-sugar. UDP-glucose dehydrogenase was still derepressed in strain MC 152. When the nonmucoid mutant was transduced to the wild-type state for this regulator gene ( <jats:italic>capR</jats:italic> <jats:sup>+</jats:sup> ), the transductant was found to accumulate less total nucleotides, and the accumulation of UDP-glucuronic acid was abolished. UDP-glucose dehydrogenase was repressed in the <jats:italic>capR</jats:italic> <jats:sup>+</jats:sup> <jats:italic>non-2</jats:italic> strain but not to the same extent that it was in the <jats:italic>capR</jats:italic> <jats:sup>+</jats:sup> strain.