Rouhiainen Leo, Vakkilainen Tanja, Siemer Berit Lumbye, Buikema William, Haselkorn Robert, Sivonen Kaarina
Department of Applied Chemistry and Microbiology, Viikki Biocenter, University of Helsinki, Helsinki, Finland.
Appl Environ Microbiol. 2004 Feb;70(2):686-92. doi: 10.1128/AEM.70.2.686-692.2004.
The cluster of microcystin synthetase genes from Anabaena strain 90 was sequenced and characterized. The total size of the region is 55.4 kb, and the genes are organized in three putative operons. The first operon (mcyA-mcyB-mcyC) is transcribed in the opposite direction from the second operon (mcyG-mcyD-mcyJ-mcyE-mcyF-mcyI) and the third operon (mcyH). The genes mcyA, mcyB, and mcyC encode nonribosomal peptide synthetases (NRPS), while mcyD codes for a polyketide synthase (PKS), and mcyG and mcyE are mixed NRPS-PKS genes. The genes mcyJ, mcyF, and mcyI are similar to genes coding for a methyltransferase, an aspartate racemase, and a D-3-phosphoglycerate dehydrogenase, respectively. The region in the first module of mcyB coding for the adenylation domain was found to be 96% identical with the corresponding part of mcyC, suggesting a recent duplication of this fragment and a replacement in mcyB. In Anabaena strain 90, the order of the domains encoded by the genes in the two sets (from mcyG to mcyI and from mcyA to mcyC) is colinear with the hypothetical order of the enzymatic reactions for microcystin biosynthesis. The order of the microcystin synthetase genes in Anabaena strain 90 differs from the arrangement found in two other cyanobacterial species, Microcystis aeruginosa and Planktothrix agardhii. The average sequence match between the microcystin synthetase genes of Anabaena strain 90 and the corresponding genes of the other species is 74%. The identity of the individual proteins varies from 67 to 81%. The genes of microcystin biosynthesis from three major producers of this toxin are now known. This makes it possible to design probes and primers to identify the toxin producers in the environment.
对鱼腥藻90株的微囊藻毒素合成酶基因簇进行了测序和表征。该区域的总大小为55.4 kb，这些基因被组织成三个假定的操纵子。第一个操纵子（mcyA - mcyB - mcyC）的转录方向与第二个操纵子（mcyG - mcyD - mcyJ - mcyE - mcyF - mcyI）和第三个操纵子（mcyH）相反。基因mcyA、mcyB和mcyC编码非核糖体肽合成酶（NRPS），而mcyD编码聚酮合酶（PKS），mcyG和mcyE是混合的NRPS - PKS基因。基因mcyJ、mcyF和mcyI分别与编码甲基转移酶、天冬氨酸消旋酶和D - 3 - 磷酸甘油酸脱氢酶的基因相似。发现mcyB第一个模块中编码腺苷化结构域的区域与mcyC的相应部分有96%的同一性，表明该片段最近发生了复制并在mcyB中被取代。在鱼腥藻90株中，两组基因（从mcyG到mcyI和从mcyA到mcyC）编码的结构域顺序与微囊藻毒素生物合成酶促反应的假定顺序共线。鱼腥藻90株中微囊藻毒素合成酶基因的顺序与另外两种蓝藻物种铜绿微囊藻和阿氏浮丝藻中发现的排列不同。鱼腥藻90株的微囊藻毒素合成酶基因与其他物种相应基因之间的平均序列匹配度为74%。各个蛋白质的同一性在67%到81%之间变化。现在已知这种毒素的三个主要产生者的微囊藻毒素生物合成基因。这使得设计探针和引物来鉴定环境中的毒素产生者成为可能。
