Hooykaas P J, den Dulk-Ras H, Ooms G, Schilperoort R A
J Bacteriol. 1980 Sep;143(3):1295-306. doi: 10.1128/jb.143.3.1295-1306.1980.
Transfer of octopine Ti plasmids to strains already carrying an octopine Ti plasmid was found to occur at the same (high) frequency as transfer to Ti plasmid lacking recipients, showing that resident Ti plasmids do not exhibit entry exclusion towards incoming Ti plasmids. The resident octopine Ti plasmid was lost by the recipient after the entrance of the incoming Ti plasmid, which is indicative of the incompatibility between the Ti plasmids. Octopine Ti plasmids were found to become established only infrequently in recipients with a nopaline Ti plasmid and, vice versa, nopaline Ti plasmids were only rarely established in recipients with an octopine Ti plasmid. Rare clones in which the incoming octopine (nopaline) Ti plasmid had been established despite the presence of a nopaline (octopine) Ti plasmid appeared to harbor cointegrates consisting of the entire incoming Ti plasmid and the entire resident Ti plasmid. The integration event invariably had occurred in a region of the plasmids that is highly conserved in evolution and that is essential for oncogenicity. These results show that octopine and nopaline Ti plasmids cannot be maintained as separate replicons by one and the same cell. Therefore, be definition, these plasmids belong to the same incompatibility group, which has been names inc Rh-1. Agrobacterial non-Ti octopine and nopaline plasmids were found to belong to another incompatibility group. The tumorigenic properties of strains harboring two different Ti plasmids, in a cointegrate structure, were indicative of the virulence genes of both of them being expressed. The agrobacterial non-Ti octopine and nopaline plasmids did not influence the virulence properties encoded by the Ti plasmid.
研究发现，章鱼碱型Ti质粒向已携带章鱼碱型Ti质粒的菌株转移的频率，与向缺乏Ti质粒的受体转移的频率相同（都很高），这表明常驻Ti质粒对进入的Ti质粒不表现出进入排斥。在进入的Ti质粒进入后，受体丢失了常驻的章鱼碱型Ti质粒，这表明Ti质粒之间存在不相容性。章鱼碱型Ti质粒很少能在携带胭脂碱型Ti质粒的受体中稳定存在，反之亦然，胭脂碱型Ti质粒也很少能在携带章鱼碱型Ti质粒的受体中稳定存在。尽管存在胭脂碱型（章鱼碱型）Ti质粒，但进入的章鱼碱型（胭脂碱型）Ti质粒仍能稳定存在的罕见克隆，似乎含有由整个进入的Ti质粒和整个常驻Ti质粒组成的共整合体。整合事件总是发生在质粒进化过程中高度保守且对致癌性至关重要的区域。这些结果表明，章鱼碱型和胭脂碱型Ti质粒不能被同一个细胞作为独立的复制子维持。因此，根据定义，这些质粒属于同一个不相容群，已被命名为Inc Rh-1。农杆菌非Ti章鱼碱型和胭脂碱型质粒属于另一个不相容群。携带两种不同Ti质粒且呈共整合体结构的菌株的致瘤特性，表明它们的毒力基因都得到了表达。农杆菌非Ti章鱼碱型和胭脂碱型质粒不影响Ti质粒编码的毒力特性。
