Cho K, Fuqua C, Winans S C
Section of Microbiology, Cornell University, Ithaca, New York 14853, USA.
J Bacteriol. 1997 Jan;179(1):1-8. doi: 10.1128/jb.179.1.1-8.1997.
By screening for octopine-inducible gene expression, we previously identified all the genes required for utilization of octopine as a source of carbon, nitrogen, and energy. They are (i) octopine oxidase, which converts octopine to arginine and pyruvate and is encoded by the ooxAB operon, (ii) arginase, which converts arginine to ornithine and urea and is encoded by arcA, (iii) ornithine cyclodeaminase, which converts ornithine to proline and ammonia and is encoded by the homologous arcB and ocd genes, and (iv) proline dehydrogenase, which converts proline to glutamate and is encoded by putA. Here we describe the regulation and localization of each of these genes. The ooxA-ooxB-ocd operon was previously shown to reside on the Ti plasmid and to be directly inducible by octopine. The arcAB operon is directly inducible by arginine, while it is induced by octopine only in strains that can convert octopine to arginine. Ornithine may also be a direct inducer of arcAB. putA is directly inducible by proline, while induction by octopine and by arginine (and probably by ornithine) requires their conversion to proline. Genetic studies indicate that arcAB and putA are localized on a conjugal genetic element. This element can be transferred to other Agrobacterium tumefaciens strains by a mechanism that does not require recA-dependent homologous recombination. Transfer of this genetic element from A. tumefaciens R10 requires at least one tra gene found on its Ti plasmid, indicating that this element is not self-transmissible but is mobilizable by the Ti plasmid. The DNA containing the arcAB and putA genes comigrates with a 243-kb linear molecular weight standard on field inversion electrophoretic gels.
通过筛选章鱼碱诱导型基因表达，我们之前鉴定出了利用章鱼碱作为碳、氮和能量来源所需的所有基因。它们是：（i）章鱼碱氧化酶，将章鱼碱转化为精氨酸和丙酮酸，由ooxAB操纵子编码；（ii）精氨酸酶，将精氨酸转化为鸟氨酸和尿素，由arcA编码；（iii）鸟氨酸环脱氨酶，将鸟氨酸转化为脯氨酸和氨，由同源的arcB和ocd基因编码；（iv）脯氨酸脱氢酶，将脯氨酸转化为谷氨酸，由putA编码。在此我们描述这些基因各自的调控和定位。之前已表明ooxA - ooxB - ocd操纵子位于Ti质粒上，并可被章鱼碱直接诱导。arcAB操纵子可被精氨酸直接诱导，而仅在能将章鱼碱转化为精氨酸的菌株中被章鱼碱诱导。鸟氨酸也可能是arcAB的直接诱导物。putA可被脯氨酸直接诱导，而被章鱼碱和精氨酸（可能还有鸟氨酸）诱导则需要它们先转化为脯氨酸。遗传学研究表明arcAB和putA位于一个接合遗传元件上。该元件可通过一种不需要recA依赖的同源重组的机制转移到其他根癌土壤杆菌菌株中。从根癌土壤杆菌R10转移这个遗传元件至少需要在其Ti质粒上发现的一个tra基因，这表明该元件不是自我可转移的，但可被Ti质粒动员。含有arcAB和putA基因的DNA在脉冲场反转电泳凝胶上与一个243 kb的线性分子量标准物共迁移。
