Negative transcriptional regulation of virulence and oncogenes of the Ti plasmid by Ros bearing a conserved C2H2-zinc finger motif.
The chromosomal ros gene in Agrobacterium tumefaciens encodes a repressor of virulence and oncogenes that are located on a resident Ti plasmid. Mutational inactivation of ros de- represses the expression of the virC and virD operons, causing premature processing and accumulation of T-DNA molecules, and the premature expression of the oncogene, ipt, leading to the synthesis of cytokinin in the bacterium rather than in the plant host cell. Ros is a 15.5 kDa protein containing a novel "eukaryotic" C(2)H(2) zinc finger. Amino acid substitutions in the finger result in the loss of binding of Ros to the ros box, a 40 bp sequence within the operator of virC/D and ipt gene promoters; and the loss of binding of a zinc ion. The ros gene is highly conserved in members of the Rhizobiaceae. Evolutionary distance tree analyses revealed distant ties to the Japanese puffer fish, Fugu rupripes rather than to plants. Interestingly, ros homologues were found in microorganisms derived from marine sources, supporting the hypothesis that ros may have originated from a marine rather than a terrestrial organism.[1]References
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