It is proposed that all mutants blocked in the de novo pathway of nicotinamide adenine dinucleotide biosynthesis be designated nad rather than nic. It is further suggested that mutants blocked in the pyridine nucleotide cycle be designated pnc. The nadB locus and a previously unidentified pur locus are cotransducible. These two loci have been mapped near minute 49 on the standard genetic map of Escherichia coli. The order of genes in that region is purC-guaB-purG-glyA-pur-nadB-tyrA-pheA.

Exogenous nicotinamide adenine dinucleotide is not utilized per se by Escherichia coli , but is converted to nicotinamide and thence to nicotinamide adenine dinucleotide via nicotinate.

Mutations affecting the biosynthesis of quinolinic acid, a precursor of nicotinamide adenine dinucleotide (NAD) in Escherichia coli K-12, are either near min 17 (nadA mutants) or near min 49 on the chromosome. These nad mutants all exhibit a phenotypic requirement for NAD or one of its immediate precursors. The mutants with lesions near min 49 can be separated into two groups based on in vitro complementation analysis. One group (nadB) exhibits complementation with nadA mutants, whereas the other group fails to do so. The latter group is tentatively designated nadR based on its regulation of the unlinked nadA gene. The nadR gene maps adjacent to nadB between purI and tyrA.

No abstract

Resistance to azaserine in Escherichia coli is the result of mutations in at least three different loci. All spontaneously arising azaserine-resistant mutants harbor a lesion in the aroP gene. However, a lesion in this gene is not solely responsible for resistance. All spontaneously arising intermediate-level azaserine-resistant mutants also harbor a lesion in a gene designated azaA, which lies near min 43 on the chromosome. High-level resistant mutants harbor lesions in the aroP and azaA genes and in a third gene designated azaB, which lies near min 69 on the chromosome. Transport studies demonstrate that mutants harboring lesions in the azaA gene are not defective in the transport of the aromatic amino acids, but that mutants which harbor lesions in the azaB gene are defective in phenylalanine transport but not in tyrosine or tryptophan transport.

TRITZ, G. J. 1974. Characterization of the rradR locus in Esclrerichia coli. .The biosynthesis of nicotinamide adenine dinucleotide (NAD) is under the genetic control of the nadRf locus. The nadR+ allele is dominant to the nadR allele in transheterogenotes, indicating that the regulation is of the positive type. Mutants of the nadR type are unable to synthesize quinolinic acid; however, they do retain the ability to convert quinolinic acid into NAD and to recycle this NAD through the pyridine nucleotide cycle. Thus, the ~radR+ locus regulates only genes involved in the biosynthesis of quinolinic acid. TRITZ, G. J. 1974. Characterization of the nadR locus in Escherichia coli. Can. J. Microbiol. 20: 205-209.La biosynthese de la nicotinamide-adenine-dinuclCotide (NAD) est sous le contrble gbnktique du locus nadR+. Chez les transhettrogenotes I'allele ~zadR+ est domlnant sur I'allele rzadR; ceci dCmontre que la regulation est du type positif. Les mutants du type riadR ne peuvent synthetiser I'acide quinolinique; cependant, ils conservent le pouvoir de transformer I'acide quinolinique en NAD et de recycler ce NAD via le cycle pyridine-nucleotide. Ainsi, le locus nndR+ rCgularise seulement les genes qui sont impliques dans la biosynthtse de I'acide quinolinique.[Traduit par le journal]

A gene involved in the synthesis of nicotinamide adenine dinucleotide has been found to be cotransducible with the genes involved in the utilization of arabinose (ara) and the biosynthesis of leucine (leu) and pantothenate (pan). Cotransduction frequency analysis places this nadC locus between leu and pan at approximately minute 1.5 on the genetic map of Escherichia coli. This gene codes for the enzyme, quinolate phosphoribosyl transferase, which catalyzes the conversion of quinolinic acid to nicotinic acid mononucleotide.The pathway for the synthesis of nicotinamide adenine dinucleotide (NAD) in Escherichia coli has been only partially defined. Recent evidence indicates that this pathway begins with the condensation of aspartic acid and a 3-carbon intermediate of glycolysis and proceeds by a series of undefined reactions to the formation of quinolinic acid (13; J. L. R. Chandler, Ph.D. Thesis, Oklahoma State Univ., Stillwater, 1969). Andreoli et al. (1) showed that a crude extract of E. coli, in the presence of 5-phosphoribosyl-1-pyrophosphate (PRPP) and quinolinic acid uniformly labeled with l4C except for the (l-carboxyl carbon, gave rise to '4CO2, labeled nicotinic acid, nicotinic acid mononucleotide, desamido-nicotinamide adenine dinucleotide (des-NAD), and NAD. Their data show that nicotinic acid is not an intermediate in the PRPP-dependent conversion of quinolinic acid to nicotinic acid mononucleotide. Nicotinic acid, therefore, is not on the de novo pathway of NAD biosynthesis, but is an intermediate in the salvage pathway of the pyridine nucleotide cycle (5). Figure 1 shows the NAD biosynthesis pathway and the pyridine nucleotide cycle as it is presently understood.In this communication, we present evidence for the chromosomal map location of a locus involved in the conversion of quinolinic acid to nicotinic acid mononucleotide in E. coli. MATERIALS AND METHODS Bacterial strains. Bacterial strains used are described in Table 1. Media. Davis and Mingioli (3) minimal medium was supplemented with 0.005 g of thiamine per liter. Hard minimal medium contained 15 g of agar per liter. Where required, the minimal medium was supplemented with 0.2 mg of the appropriate amino acid(s) per ml or 0.005 mg of nicotinic acid per ml, or both. Minimal arabinose medium contained 0.2% L-arabinose in place of glucose.Soft nutrient agar was made by adding 7.5 g of agar to 1 liter of Nutrient Broth (Difco).Mating procedure. All matings were performed on membrane filters according to the method of Matney and Achenbach (11), except that membranes supporting mating cells were incubated on soft nutrient agar plates rather than on soft minimal agar.Transduction procedure. The transduction procedure was described previously (14).Preparation of Ion exchange resin. Dowex AG1-X8 anion exchange resin [I lb (453 g)J was washed in distilled water, and the heavier particles were allowed to settle out. The finer suspended particles were decanted. The resin was washed first with 6 N HCI and then with water until neutrality was reached; this ...

Mutants of Escherichia coli defective in the biosynthesis of nicotinamide adenine dinucleotide (NAD) are able to grow in a Casamino Acids medium lacking NAD and its immediate precursors, nicotinic acid and nicotinamide. This property has allowed the development of a system to measure cross-feeding between a nadA and a nadB mutant. This system provides a means of isolating the intermediate, prequinolinic acid, as well as a biological assay for the compound. The nadB mutant feeds the nadA mutant, indicating that the nadA enzyme occurs first in the pathway and the nadB enzyme second. No cross-feeding was detected between nadA and nadC or between nadB and nadC.