The opine synthase genes carried by Ti plasmids contain all signals necessary for expression in plants.

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Abstract
Signals necessary for in vivo expression of Ti plasmid T‐DNA‐encoded octopine and nopaline synthase genes were studied in crown gall tumors by constructing mutated genes carrying various lengths of sequences upstream of the 5′ initiation site of their mRNAs. Deletions upstream of position ‐294 did not interfere with expression of the octopine synthase gene while those extending upstream of position ‐170 greatly reduced the gene expression. The estimated size of the octopine synthase promoter is therefore 295 bp. The maximal length of 5′ upstream sequences involved in the in vivo expression of the nopaline synthase gene is 261 bp. Our results also demonstrated that Ti plasmid‐derived sequences contain all signals essential for expression of opine synthase genes in plants. Expression of these genes, therefore, is independent of the direct vicinity of the plant DNA sequences and is not activated by formation of plant DNA and T‐DNA border junction.