Barratt D H, Barber L, Kruger N J, Smith A M, Wang T L, Martin C
John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom.
Plant Physiol. 2001 Oct;127(2):655-64.
Genes encoding three isoforms of sucrose synthase (Sus1, Sus2, and Sus3) have been cloned from pea (Pisum sativum). The genes have distinct patterns of expression in different organs of the plant, and during organ development. Studies of the isoforms expressed as recombinant proteins in Escherichia coli show that they differ in kinetic properties. Although not of great magnitude, the differences in properties are consistent with some differentiation of physiological function between the isoforms. Evidence for differentiation of function in vivo comes from the phenotypes of rug4 mutants of pea, which carry mutations in the gene encoding Sus1. One mutant line (rug4-c) lacks detectable Sus1 protein in both the soluble and membrane-associated fractions of the embryo, and Sus activity in the embryo is reduced by 95%. The starch content of the embryo is reduced by 30%, but the cellulose content is unaffected. The results imply that different isoforms of Sus may channel carbon from sucrose towards different metabolic fates within the cell.
已从豌豆（Pisum sativum）中克隆出编码蔗糖合酶三种同工型（Sus1、Sus2和Sus3）的基因。这些基因在植物的不同器官以及器官发育过程中具有不同的表达模式。对在大肠杆菌中表达为重组蛋白的同工型的研究表明，它们在动力学特性上存在差异。尽管差异不大，但这些特性差异与同工型之间生理功能的某种分化是一致的。体内功能分化的证据来自豌豆rug4突变体的表型，该突变体在编码Sus1的基因中携带突变。一个突变系（rug4-c）在胚胎的可溶性和膜相关部分均缺乏可检测到的Sus1蛋白，胚胎中的Sus活性降低了95%。胚胎的淀粉含量降低了30%，但纤维素含量未受影响。结果表明，Sus的不同同工型可能将蔗糖中的碳导向细胞内不同的代谢命运。
