Multiple Molecular Forms of Uridine Diphosphate Glucose Pyrophosphorylase from Salmonella typhimurium

Two genes were found to be involved in the synthesis of multiple forms of uridine diphosphate glucose pyrophosphorylase (EC 2.7.7.9) in Salmonella typhimurium. When one of them (galF) was deleted, all of the isozymic forms seen in the wild type extract (Enzymes II, IIIa, and IIIb) disappeared, and a single new form of the enzyme (Enzyme IV) was synthesized. When the other gene (galU) mutated to a leaky defective state, not only was the activity of Enzyme IV greatly reduced in the galF deletion strain but also the activities of Enzymes II, IIIa, and IIIb were very much diminished or undetectable in the strain containing the galF+ allele. Furthermore, strains containing another mutation in the galU gene produced a thermolabile Enzyme II in the presence of the galF+ allele. These results are consistent with the hypothesis that galU is a structural gene producing a polypeptide which is present in all the isozymic forms of UDP-glucose pyrophosphorylase, and that the product specified by the galF gene modifies this polypeptide so that it is converted into Enzymes II, IIIa, and IIIb.