Rossbach S, Kulpa D A, Rossbach U, de Bruijn F J
NSF Center for Microbial Ecology, Michigan State University, East Lansing 48824.
Mol Gen Genet. 1994 Oct 17;245(1):11-24. doi: 10.1007/BF00279746.
Rhizopine (L-3-O-methyl-scyllo-inosamine, 3-O-MSI) is a symbiosis-specific compound, which is synthesized in nitrogen-fixing nodules of Medicago sativa induced by Rhizobium meliloti strain L5-30. 3-O-MSI is thought to function as an unusual growth substrate for R. meliloti L5-30, which carries a locus (mos) responsible for its synthesis closely linked to a locus (moc) responsible for its degradation. Here, the essential moc genes were delimited by Tn5 mutagenesis and shown to be organized into two regions, separated by 3 kb of DNA. The DNA sequence of a 9-kb fragment spanning the two moc regions was determined, and four genes were identified that play an essential role in rhizopine catabolism (mocABC and mocR). The analysis of the DNA sequence and the amino acid sequence of the deduced protein products revealed that MocA resembles NADH-dependent dehydrogenases. MocB exhibits characteristic features of periplasmic-binding proteins that are components of high-affinity transport systems. MocC does not share significant homology with any protein in the database. MocR shows homology with the GntR class of bacterial regulator proteins. These results suggest that the mocABC genes are involved in the uptake and subsequent degradation of rhizopine, whereas mocR is likely to play a regulatory role.
根瘤碱（L-3-O-甲基-scyllo-肌醇胺，3-O-MSI）是一种共生特异性化合物，由苜蓿中华根瘤菌菌株L5-30诱导的紫花苜蓿固氮根瘤中合成。3-O-MSI被认为是苜蓿中华根瘤菌L5-30的一种特殊生长底物，该菌株携带一个负责其合成的基因座（mos），该基因座与一个负责其降解的基因座（moc）紧密相连。在此，通过Tn5诱变确定了必需的moc基因，并表明它们被组织成两个区域，由3 kb的DNA隔开。测定了跨越两个moc区域的9 kb片段的DNA序列，并鉴定出四个在根瘤碱分解代谢中起重要作用的基因（mocABC和mocR）。对DNA序列和推导的蛋白质产物的氨基酸序列分析表明，MocA类似于NADH依赖性脱氢酶。MocB表现出作为高亲和力转运系统组成部分的周质结合蛋白的特征。MocC与数据库中的任何蛋白质均无明显同源性。MocR与细菌调节蛋白的GntR类具有同源性。这些结果表明，mocABC基因参与根瘤碱的摄取和随后的降解，而mocR可能起调节作用。
