Kim J, Leustek T
Center for Agricultural Molecular Biology and Department of Food Science, Rutgers University, New Brunswick, NJ 08903-0231, USA.
Plant Mol Biol. 1996 Dec;32(6):1117-24. doi: 10.1007/BF00041395.
A cDNA clone, CGS1, encoding cystathionine gamma-synthase (CGS) from Arabidopsis thaliana was selected by complementation of CGS mutant strain of Escherichia coli (metB). Cells expressing CGS1 can grow on medium lacking Met and contain CGS enzyme activity. Genomic DNA blot analysis of A. thaliana revealed that there is a single gene homologous with CGS1. A genomic fragment carrying CGS1 was cloned and sequenced. Through combined analysis of the cDNA and genomic clone it was determined that the CGS1 coding sequence is 1692 bp, encodes a 563 amino acid, 60 kDa protein, and is interrupted by ten introns. A transcriptional initiation site was detected 260 bp 5' of the initiator codon. The predicted amino acid sequence of CGS1 contains a consensus pyridoxal phosphate-binding site and is similar to MetB of E. coli, with which it is 35 percent identical. The CGS1 product has a sequence at the amino terminus that resembles a transit peptide for localization to plastids. At least 160 amino acids from the amino terminus of the CGS1 enzyme are not essential for enzymatic activity.
通过对大肠杆菌（metB）的胱硫醚γ-合酶（CGS）突变菌株进行互补筛选，从拟南芥中获得了一个编码胱硫醚γ-合酶（CGS）的cDNA克隆CGS1。表达CGS1的细胞能够在缺乏甲硫氨酸的培养基上生长，并具有CGS酶活性。对拟南芥的基因组DNA进行印迹分析表明，存在一个与CGS1同源的单基因。携带CGS1的基因组片段被克隆并测序。通过对cDNA和基因组克隆的联合分析确定，CGS1编码序列为1692 bp，编码一个563个氨基酸、60 kDa的蛋白质，并且被10个内含子打断。在起始密码子上游260 bp处检测到一个转录起始位点。CGS1的预测氨基酸序列包含一个磷酸吡哆醛结合位点的共有序列，并且与大肠杆菌的MetB相似，同源性为35%。CGS1产物在氨基末端有一个类似于定位到质体的转运肽的序列。CGS1酶氨基末端至少160个氨基酸对于酶活性不是必需的。
