Multiple domains exist within the upstream activator sequence of the octopine synthase gene.

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Abstract
It is known that a 16-base pair palindrome (ACGTAAGCGCTTACGT) located upstream of the ocs gene can activate a maize adh1 promoter in a transient expression system [Ellis et al. (1987). EMBO J. 6, 11-16: Ellis et al. (1987). EMBO J. 6, 3203-3208]. We haved determined that this palindrome is also essential for ocs promoter activity in tobacco calli. In addition, sequences immediately adjacent to this palindrome, both 5'' and 3'', modulate its activity. The palindrome is sensitive to the differentiated state of the plant cells in which it resides; it is active in calli and the leaves of small shoots but is inactive in the leaves of rooted plants. We have tested upstream sequences from two other T-DNA genes that have homology to this palindrome for their ability to activate the octopine synthase promoter in tobacco calli. The upstream region from the mannopine synthase gene can activate the octopine synthase promoter, but an upstream region from the gene implicated in octopine and nopaline secretion cannot activate the promoter.