An enhancer-like element present in the promoter of a T-DNA gene from the Ti plasmid of Agrobacterium tumefaciens

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The promoter of the 780 gene of T-right [Thomashow, M., Nutter, R., Montoya, A., Gordon, M. & Nester, E. (1980) Cell 19, 729-739] from Agrobacterium tumefaciens Ti plasmid (pTi15955) was shown to contain an upstream cis-acting element (activator) having enhancer-like properties. To characterize the properties of this promoter element, it was placed in both polarities, upstream and downstream of a Δ-37 deletion mutant of the 780 gene. The Δ-37 deletion contains the entire 780 gene with the 5′ flanking sequences deleted upstream of TATA to -37. The effect of the activator on in vivo transcriptional activity was assessed by S1 nuclease mapping utilizing a homologous reference gene as an internal standard. Transcript levels from sunflower crown gall tumors were between 127% and 90% of the wild-type 780 gene depending on the polarity of the activator element when placed directly upstream to the 780 gene Δ-37 promoter. Repositioning the activator element 613 base pairs further upstream increased transcription by 2-fold regardless of polarity. However, the activator element did not promote transcription when placed in either polarity ≈200 base pairs downstream of the poly(A) addition site. Upstream promoter fragments (TATA-distal) from the octopine synthase (ocs) and agropine synthase (ags) genes were also tested for activation of the Δ-37 construction. The ocs sequences activated transcription of the Δ-37 deletion to 14% of wild-type levels when placed upstream in the B (reverse) orientation. All other constructions with the ocs and ags sequences showed no enhancement of promoter activity.

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