Studies on the female sterile mutant rudimentary of Drosophila melanogaster. II. An analysis of aspartate transcarbamylase and dihydroorotase activities in wild-type and rudimentary strains

The EGF repeat-specific O-GlcNAc-transferase Eogt interacts with notch signaling and pyrimidine metabolism pathways in Drosophila

The O-GlcNAc transferase Eogt modifies EGF repeats in proteins that transit the secretory pathway, including Dumpy and Notch. In this paper, we show that the Notch ligands Delta and Serrate are also substrates of Eogt, that mutation of a putative UDP-GlcNAc binding DXD motif greatly reduces enzyme activity, and that Eogt and the cytoplasmic O-GlcNAc transferase Ogt have distinct substrates in Drosophila larvae. Loss of Eogt is larval lethal and disrupts Dumpy functions, but does not obviously perturb Notch signaling. To identify novel genetic interactions with eogt, we investigated dominant modification of wing blister formation caused by knock-down of eogt. Unexpectedly, heterozygosity for several members of the canonical Notch signaling pathway suppressed wing blister formation. And importantly, extensive genetic interactions with mutants in pyrimidine metabolism were identified. Removal of pyrimidine synthesis alleles suppressed wing blister formation, while removal of uracil catabolism alleles was synthetic lethal with eogt knock-down. Therefore, Eogt may regulate protein functions by O-GlcNAc modification of their EGF repeats, and cellular metabolism by affecting pyrimidine synthesis and catabolism. We propose that eogt knock-down in the wing leads to metabolic and signaling perturbations that increase cytosolic uracil levels, thereby causing wing blister formation.

Construction of a cDNA to the hamster CAD gene and its application toward defining the domain for aspartate transcarbamylase

cDNA complementary to hamster mRNA encoding the CAD protein, a multifunctional protein which carries the first three enzymes of pyrimidine biosynthesis, was constructed. The longest of these recombinants (pCAD142) covers 82% of the 7.9-kilobase mRNA. Portions of the cDNA were excised and replaced by a lac promoter-operator-initiation codon segment. The resultant plasmids were transfected into an Escherichia coli mutant defective in aspartate transcarbamylase, the second enzyme of the pathway. Complementation of the bacterial defect was observed with as little as 2.2 kilobases of cDNA sequence, corresponding to the 3' region of the mRNA. DNA sequencing in this region of the hamster cDNA reveals stretches which are highly homologous to the E. coli gene for the catalytic subunit of aspartate transcarbamylase; other stretches show no homology. The highly conserved regions probably reflect areas of protein structure critical to catalysis, while the nonconserved regions may reflect differences between the quaternary structures of E. coli and mammalian aspartate transcarbamylases, one such difference being that the bacterial enzyme in its native form is allosterically regulated and the mammalian enzyme is not.

Construction of a cDNA to the hamster CAD gene and its application toward defining the domain for aspartate transcarbamylase

cDNA complementary to hamster mRNA encoding the CAD protein, a multifunctional protein which carries the first three enzymes of pyrimidine biosynthesis, was constructed. The longest of these recombinants (pCAD142) covers 82% of the 7.9-kilobase mRNA. Portions of the cDNA were excised and replaced by a lac promoter-operator-initiation codon segment. The resultant plasmids were transfected into an Escherichia coli mutant defective in aspartate transcarbamylase, the second enzyme of the pathway. Complementation of the bacterial defect was observed with as little as 2.2 kilobases of cDNA sequence, corresponding to the 3' region of the mRNA. DNA sequencing in this region of the hamster cDNA reveals stretches which are highly homologous to the E. coli gene for the catalytic subunit of aspartate transcarbamylase; other stretches show no homology. The highly conserved regions probably reflect areas of protein structure critical to catalysis, while the nonconserved regions may reflect differences between the quaternary structures of E. coli and mammalian aspartate transcarbamylases, one such difference being that the bacterial enzyme in its native form is allosterically regulated and the mammalian enzyme is not.

Partial cDNA sequence to a hamster gene corrects defect in Escherichia coli pyrB mutant

The first three enzymes of pyrimidine biosynthesis (carbamoyl-phosphate synthetase, aspartate carbamoyl-transferase, and dihydro-orotase) are carried on a multifunctional protein in mammalian cells and are on separate proteins in bacteria. A plasmid containing a cDNA sequence corresponding to 80% of a hamster mRNA for this protein was transformed into Escherichia coli mutants lacking aspartate carbamoyltransferase (pyrB) or dihydro-orotase (pyrC). Only pyrB transformants were able to grow in the absence of uracil. Plasmid recovered from primary transformants was similar in size to the original plasmid and could yield prototrophs after secondary transformation of E. coli pyrB mutants. When cell extracts were prepared from pyrB transformants, high levels of aspartate carbamoyltransferase activity were found, and the enzyme had properties identical to the mammalian enzyme, including lack of allosteric regulation, precipitation by antiserum specific to the hamster multifunctional protein, and presence of a strong aggregation center. These results demonstrate that (i) a partial hamster protein can complement E. coli defective in pyrimidine biosynthesis, (ii) the order of the enzyme domains of the multifunctional protein is likely to be NH2-dihydro-orotase-carbamoyl-phosphate synthetase-aspartate carbamoyltransferase-COOH, and (iii) the enzyme domains appear to be self-contained at the DNA and protein levels. The protocol described here may be a general means for studying the domains of multifunctional proteins and for isolating other mammalian genes for which bacterial mutants have been prepared. It also permits study of the structure and function of the same gene in both prokaryotic and eukaryotic cells and may provide new insight into the evolution of complex genes.

Cytogenetic analysis of the 2B3-4--2B11 region of the X-chromosome of Drosophila melanogaster. I. Cytology of the region and mutant complementation groups

There are, at least, 11 distinct single bands and one real doublet in the region 2B1-2--2C1-2 of the X-chromosome of Drosophila melanogaster. This figure coincides with that in Bridges' revised map with most of the "doublet" bands being artifacts. Three puffs appear in the region. The early ecdysone-specific puff 2B5-6, small at PS(puffing stage) 1, increases sharply at PS 2. The late ecdysone-specific puff 2C1-2 appears at PS 4--5. At PS 9--10, when 2B5-6 disappears completely and 2C1-2 decreases, a third puff at 2B11 appears. None of these puffs is active at PS 11. Morphological analysis of puff appearance and autoradiographic study of 3H-uridine incorporation into chromosomes carrying rearrangements within the 2B region suggest that the early ecdysone-specific puff derives from bands 2B5 and may be 2B6, while the neighbouring bands 2B1-4, and 2B7-10 do not show appreciable transcription at the investigated stages. There are 42 mutations affecting viability in the region where the 2B5-6 puff is located. The mutations belong to 6 complementation groups; two of the groups dor and swi, are independent while the rest are overlapped by several lethal mutations (overlapping complex.) Mutants of the different groups have series of similar characteristics: temperature sensitivity, dose sensitivity, larva-pupal lethality and similar morphological abnormalities. It can be assumed that there is a functionally linked cluster of genes within the region 2B. Complementation groups br, rbp, l(1)pp-1, l(1)pp-2 (overlapping complex) have been located by rearrangements in very narrow cytological limit 2B3-4--2B5 that is in the area of developing puff. Two other loci dor and swi are situated some to the right of 2B5.

Biochemical genetic analysis of pyrimidine biosynthesis in mammalian cells: III. Association of carbamyl phosphate synthetase, aspartate transcarbamylase, and dihydroorotase in mutants of cultured Chinese hamster cells

Carbamyl phosphate synthetase (EC 2.7.2.9), aspartate transcarbamylase (EC 2.1.3.2), and dihydroorotase (EC 3.5.2.3), the first three enzymes in de novo pyrimidine synthesis in Chinese hamster ovary cell strain Kl (CHO-Kl), cose diment through a glycerol gradient. When an extract from Urd- A, a pyrimidine-requiring auxotroph reduced in all three activities, is run on a glycerol gradient, the enzyme activities appear in two peaks higher in the gradient, a peak of aspartate transcarbamylase separated from a peak of carbamyl phosphate synthetase and dihydroorotase. Revertants of Urd- A have increased activity of all three enzymes and give glycerol gradient patterns similar to either CHO-Kl or Urd- A. The gradient pattern for Urd- A and some of its revertants can be mimicked by treating the CHO-Kl cell extract with trypsin. Hybrids made between a CHO-Kl purine-requiring auxotroph (Ade- C) and a Urd- A revertant gave a glycerol gradient pattern which is a composite of the CHO-Kl and revertant patterns. A model is presented for the structure of this multifunctional protein.