Hwang I, Li P L, Zhang L, Piper K R, Cook D M, Tate M E, Farrand S K
Department of Plant Pathology, University of Illinois at Urbana-Champaign 61801.
Proc Natl Acad Sci U S A. 1994 May 24;91(11):4639-43. doi: 10.1073/pnas.91.11.4639.
Conjugal transfer of the nopaline-type Agrobacterium Ti plasmid pTiC58 is regulated by a transcriptional activator, TraR, and a diffusible signal molecule, conjugation factor (CF). CF is a member of a family of substituted homoserine lactones (HSLs) that act as coinducers for regulating gene expression in diverse Gram-negative bacteria by a mechanism called autoinduction. In Vibrio fischeri HSL production is conferred by the luxI gene. Homologues of this gene are responsible for HSL production by other Gram-negative bacteria. A gene that we call traI, conferring production of material with CF activity, was localized to a 1-kb region at the upstream end of tra3 of pTiC58. Spectroscopy showed that the activity was authentic CF. Sequence analysis showed that traI could encode a protein of 211 amino acids, TraI, that is related to the proteins responsible for HSL production by other bacteria. A second, partial open reading frame immediately downstream of traI could encode a protein related to TrbB of plasmid RP4, which is required for conjugal transfer. Transcription of traI and of the downstream tra3 genes requires TraR and CF and initiates from the traI promoter. The results show that traI is responsible for CF production, that it is the first gene of the tra3 operon, and that expression of this operon is regulated by autoinduction.
胭脂碱型农杆菌Ti质粒pTiC58的接合转移受转录激活因子TraR和一种可扩散信号分子——接合因子（CF）调控。CF是取代型高丝氨酸内酯（HSLs）家族的一员，HSLs作为共诱导剂，通过一种称为自诱导的机制调控多种革兰氏阴性菌中的基因表达。在费氏弧菌中，luxI基因负责HSL的产生。该基因的同源物在其他革兰氏阴性菌中负责HSL的产生。我们将一个赋予具有CF活性物质产生能力的基因命名为traI，它定位于pTiC58的tra3上游末端的一个1 kb区域。光谱分析表明该活性物质是真正的CF。序列分析显示，traI可以编码一个由211个氨基酸组成的蛋白质TraI，它与其他细菌中负责HSL产生的蛋白质相关。traI下游紧邻的第二个部分开放阅读框可以编码一个与质粒RP4的TrbB相关的蛋白质，TrbB是接合转移所必需的。traI和下游tra3基因的转录需要TraR和CF，并从traI启动子起始。结果表明，traI负责CF的产生，它是tra3操纵子的第一个基因，并且该操纵子的表达受自诱导调控。
