Luttinger A L, Springer A L, Schmid M B
Department of Molecular Biology, Princeton University, NJ 08544.
New Biol. 1991 Jul;3(7):687-97.
Thirteen conditional lethal mutations in genes of Salmonella typhimurium map at the clmF locus and affect both viability and the faithful partitioning of daughter nucleoids. These mutations have now been divided into three complementation groups by using cloned fragments of S. typhimurium DNA and renamed parC, parE, and parF. The proteins produced from the cloned fragments predict that ParC is an 85-kD protein, ParE is 75 kD in size, and ParF, 27 kD. The parE gene is about 5 kb upstream of the parC gene, and parC is just upstream of parF. Genes situated between parC and parE produce at least two proteins of unknown function. The DNA sequence of the S. typhimurium parC gene was determined and has 56% homology with the first 1400 base pairs of the Escherichia coli gryA gene, which encodes the A subunit of DNA gyrase, and 85% homology with the E. coli parC gene. Despite the strong homology between gryA and parC, these two genes cannot substitute for one another. The DNA sequence of the S. typhimurium parF gene was determined and predicts a protein with a hydrophobic N terminus. The ParF protein may interact with ParC and ParE to anchor these proteins to the membrane. These results raise questions about the relative roles of gyrase and ParCEF in nucleoid decatenation. In addition, the parC and gyrA genes provide an example of the evolution of essential functions by gene duplication.
鼠伤寒沙门氏菌基因中的13个条件致死突变定位于clmF位点，影响生存能力和子代类核的准确分配。现在，利用鼠伤寒沙门氏菌DNA的克隆片段，这些突变已被分为三个互补群，并重新命名为parC、parE和parF。从克隆片段产生的蛋白质预测，ParC是一种85-kD的蛋白质，ParE大小为75 kD，ParF为27 kD。parE基因在parC基因上游约5 kb处，parC就在parF上游。位于parC和parE之间的基因产生至少两种功能未知的蛋白质。测定了鼠伤寒沙门氏菌parC基因的DNA序列，它与编码DNA促旋酶A亚基的大肠杆菌gryA基因的前1400个碱基对有56%的同源性，与大肠杆菌parC基因有85%的同源性。尽管gryA和parC之间有很强的同源性，但这两个基因不能相互替代。测定了鼠伤寒沙门氏菌parF基因 的DNA序列，预测其蛋白质的N端具有疏水性。ParF蛋白可能与ParC和ParE相互作用，将这些蛋白质锚定在膜上。这些结果引发了关于促旋酶和ParCEF在类核解连环中的相对作用的问题。此外，parC和gyrA基因提供了一个通过基因复制实现基本功能进化的例子。
