Regulatory Sequences Control Gene Expression
Role of 3' Sequences
Role of 3' Sequences in Gene ExpressionAll of the discussions so far have highlighted the role of the promoter in gene expression. But can other regions of the gene also play a role in gene expression? Experiments have shown that 3' sequences and introns can both affect gene expression.
The effect 3' sequences of a plant proteinase inhibitor were analyzed in 1987 (PNAS 84:744). Proteinase inhibitors are induced upon plant injury and act to prevent cell degrading enzymes released by insects from damaging the plant. The genes for these proteins have been isolated, and the controlling sequences were linked to reporter genes and introduced into transgenic plants. The following constructs were made:
Proteinase Inhibitor Promoter --- CAT --- PI 3'
Proteinase Inhibitor Promoter --- CAT --- 6b 3'
(PI is the 3' sequence from the proteinase inhibitor gene. 6b is a gene from the A. tumefaciens A6 Ti-plasmid that is expressed in galls.)
Transgenic plants were derived with each of the two constructs and wounded to determine what the response will be. The following conclusions were drawn from these experiments.