Chen J, Post-Beittenmiller D
Plant Biology Division, Samuel Noble Foundation, Ardmore, OK 73402, USA.
Gene. 1996 Dec 5;182(1-2):45-52. doi: 10.1016/s0378-1119(96)00472-6.
3-Ketoacyl-acyl carrier protein synthase III (KAS III) catalyzes the initial condensation of malonyl-acyl carrier protein (ACP) with acetyl-CoA in plant and bacterial fatty acid biosynthesis. The first cDNA clone encoding KAS III from a monocot is reported here. A cDNA clone was isolated from a leek epidermal cDNA library by screening with spinach and Arabidopsis heterologous probes from KAS III cDNA clones. When expressed in Escherichia coli, the cloned enzyme was able to catalyze the expected condensation reaction, was insensitive to cerulenin (100 microM) and cross-reacted with spinach KAS III antibody. The 1476-bp cDNA clone contained a 1206-bp open reading frame which encoded a 402-amino acid polypeptide. The deduced amino acid sequence showed significant similarities to other KAS IIIs although the leek sequence had some notable differences in regions otherwise completely conserved in dicots. Northern blot analyses indicated that KAS III transcript levels were similar in leaf epidermis and parenchyma, although developmental changes in transcript levels differed between these two tissues. In addition, leek KAS III was expressed in a manner comparable to leek oleoyl-ACP thioesterase (OTE), another enzyme of fatty acid biosynthesis, in both tissues.
3-酮酰基-酰基载体蛋白合酶III（KAS III）在植物和细菌脂肪酸生物合成中催化丙二酸单酰-酰基载体蛋白（ACP）与乙酰辅酶A的初始缩合反应。本文报道了首个从单子叶植物中克隆得到的编码KAS III的cDNA。通过用菠菜和拟南芥KAS III cDNA克隆的异源探针筛选，从韭菜表皮cDNA文库中分离出一个cDNA克隆。当在大肠杆菌中表达时，克隆的酶能够催化预期的缩合反应，对浅蓝菌素（100微摩尔）不敏感，并与菠菜KAS III抗体发生交叉反应。这个1476碱基对的cDNA克隆包含一个1206碱基对的开放阅读框，编码一个402个氨基酸的多肽。推导的氨基酸序列与其他KAS III有显著相似性，尽管韭菜序列在双子叶植物中完全保守的区域有一些明显差异。Northern杂交分析表明，KAS III转录本水平在叶表皮和薄壁组织中相似，尽管这两个组织中转录本水平的发育变化有所不同。此外，韭菜KAS III在这两个组织中的表达方式与韭菜油酰-ACP硫酯酶（OTE）相当，后者是脂肪酸生物合成中的另一种酶。
