The virulence (vir) genes of Agrobacterium tumefaciens are induced by low-molecular-weight phenolic compounds and monosaccharides through a two-component regulatory system consisting of the VirA and VirG proteins. However, it is not clear how the phenolic compounds are sensed by the VirA/VirG system. We tested the vir-inducing abilities of 15 different phenolic compounds using four wildtype strains ofA. tumefaciens-KU12, C58, A6, and Bo542. We analyzed the relationship between structures of the phenolic compounds and levels of vir gene expression in these strains. In strain KU12, vir genes were not induced by phenolic compounds containing 4'-hydroxy, 3'-methoxy, and 5'-methoxy groups, such as acetosyringone, which strongly induced vir genes of the other three strains. On the other hand, vir genes of strain KU12 were induced by phenolic compounds containing only a 4'-hydroxy group, such as 4-hydroxyacetophenone, which did not induce vir genes of the other three strains. The vir genes of strains KU12, A6, and Bo542 were all induced by phenolic compounds containing 4'-hydroxy and 3'-methoxy groups, such as acetovanillone. By transferring different Ti plasmids into isogenic chromosomal backgrounds, we showed that the phenolic-sensing determinant is associated with Ti plasmid. Subcloning Table 2 show that the induction response to different phenolic compounds varies among the different strains.Under our standard induction conditions, vir genes in both the octopine-type strain A6 and the succinamopine-type strain Bo542 were strongly induced by all phenolic compounds in group A. The nopaline-type strain C58 showed a moderate level of vir gene induction by acetosyringone and sinapinic acid. However, no response to syringaldehyde, syringic acid, and 2,6-dimethoxyphenol was observed. Surprisingly, we found that all phenolic compounds in group A, including acetosyringone, the most commonly used vir gene inducer in the laboratory, were unable to induce the vir genes of strain KU12. All strains except C58 responded to acetovanillone and ferulic acid of group B, and strains KU12 and Bo542 were both induced by guaiacol. However, only strain Bo542 was induced by vanillin of group B. In our hands, strain A6 was not induced by vanillin, a phenolic compound classified as a strong vir gene inducer by Melchers et al. (29) using A. tumefaciens strain LBA2516, which contains an octopine-type Ti plasmid, pTiB6, that is closely related to pTiA6 (12). The reason for this discrepancy is not clear. Of special interest is the observation that the vir genes of strain KU12 were highly induced by a group of compounds in group C that lack both methoxy groups. These compounds included 4-hydroxyacetophenone, p-coumaric acid, and phenol, which had previously been reported to be non-vir gene inducers (29). In support of this latter report, the three otherA. tumefaciens strains were indeed not induced by the phenolic compounds in group C.We tested vir gene induction by other phenolic compounds that lacked the hydroxyl group at the R4 posi...

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We reported previously that chloroplast DNA binding factors bind to the rbcL promoter R2 (-33 to 229 from ATG) region in Zea mays. In this study, we investigated transcriptional activity in the high salt extracts of chloroplast, and identified rbcL R2 region-specific binding proteins in high-salt extracts. In-vitro transcription and dot blot assays revealed that the extract was transcriptionally active. An electrophoretic mobility shift assay (EMSA) showed that R2 region Binding Factors I and 2 (named RBF-1, 2) bound specifically to the R2 region. RBF-1 and 2 were precipitated in 0 to 34% and 34 to 51% ammonium sulfate fraction, respectively; their binding activities were detected in 0.2 M and 0.4 M KCI fractions of DEAE cellulose chromatography, respectively. RBF-1 and RBF-2 were purified to about 140-and 66-fold from the chloroplast high-salt extract, respectively, and had specific binding activity to the R2 region. These factors may play an important role in regulating the transcription of rbcL.

Two protein factors, isolated from S-100 of maize shoots, were found to be required not only for a "Mg(2+) shift" for poly U-dependent polymerization of phenylalanine, but also for polyphenylalanine synthesis. They seem to be crude preparations of EF-1 and EF-2. The poly U-directed amino acid incorporation by washed ribosomes was completely dependent upon these factors.