Lyi S M, Jafri S, Winans S C
Section of Microbiology, Cornell University, Ithaca, NY 14853, USA.
Mol Microbiol. 1999 Jan;31(1):339-47. doi: 10.1046/j.1365-2958.1999.01178.x.
Octopine-type Ti plasmids such as pTi15955, pTiA6 and pTiR10 direct the catabolism of at least eight compounds called opines that are released from crown gall tumours. Four of these compounds are denoted mannityl opines, each of which possesses a D-mannityl substituent on the nitrogen atom of either glutamate or glutamine. We have analysed a 20 kb region of the Ti plasmid pTi15955 that is required for the catabolism of two such opines, mannopinic acid and agropinic acid. A total of 12 genes in four operons were identified by DNA sequence analysis. Transposons Tn5lacZ and MudK were used to mutagenize these genes and to create aga-lacZ and moa-lacZ translational fusions. The expression of all fusions was induced by agropinic acid and by mannopinic acid. One of these four operons encodes an agropinic acid permease, whereas a second one encodes a mannopinic acid permease. A third operon contains three genes encoding probable catabolic enzymes, two of which (AgaF and AgaG) are thought to convert agropinic acid to mannopinic acid, while the third (AgaE) probably converts mannopinic acid to mannose and glutamate. AgaE resembles a bacterial amino acid deaminase, whereas AgaF and AgaG resemble two bacterial proteins that together catabolize substituted hydantoins, whose chemical structure resembles that of agropinic acid. The remaining operon encoded the MoaR protein, a negative regulator of itself and of the other three operons.
章鱼碱型Ti质粒，如pTi15955、pTiA6和pTiR10，指导至少八种被称为冠瘿碱的化合物的分解代谢，这些化合物从冠瘿瘤中释放出来。其中四种化合物被称为甘露碱型冠瘿碱，每种在谷氨酸或谷氨酰胺的氮原子上都有一个D-甘露糖基取代基。我们分析了Ti质粒pTi15955的一个20 kb区域，该区域是两种这样的冠瘿碱——甘露碱酸和农杆碱酸分解代谢所必需的。通过DNA序列分析在四个操纵子中总共鉴定出12个基因。转座子Tn5lacZ和MudK被用于诱变这些基因，并创建aga-lacZ和moa-lacZ翻译融合体。所有融合体的表达都由农杆碱酸和甘露碱酸诱导。这四个操纵子中的一个编码一种农杆碱酸通透酶，而另一个编码一种甘露碱酸通透酶。第三个操纵子包含三个编码可能的分解代谢酶的基因，其中两个（AgaF和AgaG）被认为将农杆碱酸转化为甘露碱酸，而第三个（AgaE）可能将甘露碱酸转化为甘露糖和谷氨酸。AgaE类似于一种细菌氨基酸脱氨酶，而AgaF和AgaG类似于两种共同分解代谢取代乙内酰脲的细菌蛋白，其化学结构类似于农杆碱酸。其余的操纵子编码MoaR蛋白，它是自身以及其他三个操纵子的负调节因子。
