RESUMEN
We sequenced the virD-virE, virE-virF, and virF-T-DNA intergenic regions of an octopine Ti plasmid. Four newly described genes were induced by the vir gene inducer acetosyringone, two of which are conserved in the nopaline-type Ti plasmid pTiC58. One gene resembles a family of phosphatase genes. Each of these genes is dispensable for tumorigenesis.
Asunto(s)
Arginina/análogos & derivados , Plásmidos/genética , Regulón , Rhizobium/genética , Acetofenonas/farmacología , Secuencia de Aminoácidos , Arginina/metabolismo , Operón Lac , Datos de Secuencia Molecular , Plantas/microbiología , Proteínas Recombinantes de Fusión , Rhizobium/patogenicidad , Endonucleasas Específicas del ADN y ARN con un Solo Filamento/metabolismo , Virulencia/genéticaRESUMEN
We have determined the DNA sequences of two unlinked regions of octopine-type Ti plasmids that contain genes required for conjugal transfer. Both regions previously were shown to contain sequences that hybridize with tra genes of the nopaline-type Ti plasmid pTiC58. One gene cluster (designated tra) contains a functional oriT site and is probably required for conjugal DNA processing, while the other gene cluster (designated trb) probably directs the synthesis of a conjugal pilus and mating pore. Most predicted Tra and Trb proteins show relatively strong sequence similarity (30 to 50% identity) to the Tra and Trb proteins of the broad-host-range IncP plasmid RP4 and show significantly weaker sequence similarity to Vir proteins found elsewhere on the Ti plasmid. An exception is found in the Ti plasmid TraA protein, which is predicted to be a bifunctional nickase-helicase that has no counterpart in IncP plasmids or among Vir proteins but has homologs in at least six other self-transmissible and mobilizable plasmids. We conclude that this Ti plasmid tra system evolved by acquiring genes from two or three different sources. A similar analysis of the Ti plasmid vir region indicates that it also evolved by appropriating genes from at least two conjugal transfer systems. The widely studied plasmid pTiA6NC previously was found to be nonconjugal and to have a 12.65-kb deletion of DNA relative to other octopine-type Ti plasmids. We show that this deletion removes the promoter-distal gene of the trb region and probably accounts for the inability of this plasmid to conjugate.
Asunto(s)
Agrobacterium tumefaciens/genética , Arginina/análogos & derivados , Proteínas Bacterianas , Conjugación Genética/genética , Genes Bacterianos , Plásmidos/genética , Agrobacterium tumefaciens/patogenicidad , Secuencia de Aminoácidos , Proteínas de la Membrana Bacteriana Externa/genética , Secuencia de Bases , Evolución Biológica , Proteínas Fimbrias , Regulación Bacteriana de la Expresión Génica , Técnicas de Transferencia de Gen , Modelos Genéticos , Datos de Secuencia Molecular , Familia de Multigenes , Plásmidos/clasificación , Origen de Réplica , Mapeo Restrictivo , Homología de Secuencia de Aminoácido , Virulencia/genéticaRESUMEN
Many bacteria, including several pathogens of plants and humans, use a pheromone called an autoinducer to regulate gene expression in a cell density-dependent manner. Agrobacterium autoinducer [AAI, N-(3-oxo-octanoyl)-L-homoserine lactone] of A. tumefaciens is synthesized by the Tral protein, which is encoded by the tumor-inducing plasmid. Purified hexahistidinyl-Tral (H6-Tral) used S-adenosylmethionine to make the homoserine lactone moiety of AAI, but did not use related compounds. H6-Tral used 3-oxo-octanoyl-acyl carrier protein to make the 3-oxo-octanoyl moiety of AAI, but did not use 3-oxo-octanoyl-coenzyme A. These results demonstrate the enzymatic synthesis of an autoinducer through the use of purified substrates.
