Hughes K T, Roth J R, Olivera B M
Department of Microbiology, University of Washington, Seattle 98195.
Genetics. 1991 Apr;127(4):657-70. doi: 10.1093/genetics/127.4.657.
The nadC gene of Salmonella encodes the pyridine biosynthetic enzyme PRPP-quinolinate phosphoribosyltransferase. Using a combination of genetic techniques, a deletion map for the Salmonella nadC gene has been generated which includes over 100 point mutants and 18 deletion intervals. The nadC alleles obtained by hydroxylamine mutagenesis include those suppressed by either amber, ochre, or UGA nonsense suppressors as well as alleles suppressed by the missense suppressor, sumA. Deletions were obtained by three separate protocols including spontaneous selection for loss of the nearby aroP gene, recombination between aroP::MudA and nadC::MudA insertion alleles, and selection for spontaneous loss of tetracycline resistance in a nearby guaC::Tn10dTc insertion mutant allele. The nadC mutants comprise one complementation group and the nadC+ allele is dominant to simple, nadC auxotrophic mutant alleles. Intragenic complementation of two nadC alleles, nadC493 and nadC494, mapping to deletion intervals 17 and 18, respectively, suggests that nadC encodes a multimeric enzyme. Both nadC and the nearby aroP locus are transcribed counterclockwise on the standard genetic map of Salmonella, in opposite orientation to the direction of chromosome replication.
沙门氏菌的nadC基因编码吡啶生物合成酶PRPP - 喹啉酸磷酸核糖转移酶。通过结合多种遗传技术，构建了沙门氏菌nadC基因的缺失图谱，其中包括100多个点突变体和18个缺失区间。通过羟胺诱变获得的nadC等位基因包括那些可被琥珀色、赭石色或UGA无义抑制子抑制的等位基因，以及可被错义抑制子sumA抑制的等位基因。通过三种不同的方案获得缺失，包括自发选择附近aroP基因的缺失、aroP::MudA和nadC::MudA插入等位基因之间的重组，以及在附近guaC::Tn10dTc插入突变体等位基因中自发选择四环素抗性的丧失。nadC突变体组成一个互补群，nadC+等位基因对简单的nadC营养缺陷型突变体等位基因呈显性。分别定位到缺失区间17和18的两个nadC等位基因nadC493和nadC494的基因内互补表明，nadC编码一种多聚体酶。在沙门氏菌的标准遗传图谱上，nadC和附近的aroP基因座均逆时针转录，与染色体复制方向相反。
