Derepression of GDP-α-D-Mannose and UDP-Glucose Pyrophosphorylases by a Regulator Gene Mutation; Episomal Dominance in Partial Diploids

Mutants of Escherichia coli K12 at the capR locus are overproduce capsular polysaccharide, and are derepressed for synthesis of several enzymes involved in capsular polysaccharide synthesis(1-3) including GDP-mannose pyrophosphorylase.(8) UDP-glucose pyrophosphorylase is also derepressed in a haploid capR9 mucoid mutant. Heterozygous mucoid partial diploids with the capR9 allele on the episome and the wild-type (capR(+)) allele on the chromosome (F'capR9/capR(+)) are derepressed for UDP-glucose pyrophosphorylase and GDP-mannose pyrophosphorylase, while the reciprocal nonmucoid heterozygotes (F'capR(+)/capR9) are repressed for these enzymes. These results provide evidence that the episomal capR allele is dominant with respect to synthesis of these two enzymes.