Schachman H K, Pauza C D, Navre M, Karels M J, Wu L, Yang Y R
Proc Natl Acad Sci U S A. 1984 Jan;81(1):115-9. doi: 10.1073/pnas.81.1.115.
Recent genetic studies of the pyrB locus of Escherichia coli resulted in the characterization of 29 mutant strains harboring defects in the structural gene that encodes the catalytic chains of aspartate transcarbamoylase (carbamoylphosphate: L-aspartate carbamoyltransferase, EC 2.1.3.2). Three alleles, pyrB554, pyrB730, and pyrB748, have been cloned, and their nucleotide sequences have been determined along with that of the wild-type pyrBI operon in order to locate the sites of the alterations in the catalytic chains. Missense mutation pyrB554 leads to replacement of serine-52 by phenylalanine, and the inactive mutant enzyme has properties similar to those of wild-type aspartate transcarbamoylase. The amber mutation pyrB730 results in unstable truncated polypeptide chains 27 amino acids shorter than wild-type chains. Deletion mutation pyrB748 causes the removal of 181 amino acids. Combining these results with knowledge of the crystallographic structure of the wild-type enzyme provides a basis for tentative structural mechanisms for the observed complementation behavior of the mutant proteins.
最近对大肠杆菌天冬氨酸转氨甲酰酶基因座（pyrB）的遗传学研究，鉴定出了29个突变菌株，这些菌株在编码天冬氨酸转氨甲酰酶（氨甲酰磷酸：L-天冬氨酸氨甲酰转移酶，EC 2.1.3.2）催化链的结构基因中存在缺陷。已克隆出三个等位基因pyrB554、pyrB730和pyrB748，并测定了它们的核苷酸序列以及野生型pyrBI操纵子的核苷酸序列，以便确定催化链中改变位点的位置。错义突变pyrB554导致丝氨酸-52被苯丙氨酸取代，失活的突变酶具有与野生型天冬氨酸转氨甲酰酶相似的特性。琥珀突变pyrB730导致比野生型链短27个氨基酸的不稳定截短多肽链。缺失突变pyrB748导致181个氨基酸的缺失。将这些结果与野生型酶的晶体结构知识相结合，为观察到的突变蛋白互补行为的初步结构机制提供了基础。
