A Mutant Lectin Gene 1s Rescued from an lnsertion Element That Blocks Its Expression

The soybean lectin gene Lel encodes a prevalent seed protein and is highly regulated during the life cycle. The mutant lectin gene allele /e7 is not transcribed detectably, contains a 3.541 Tgml insertion element within its coding region 0.6 kb 3' to the transcription start site, and leads to a lectinless phenotype. To determine whether the Tgml element or a secondary mutation was responsible for repressing /e7 gene transcription, we eliminated the insertion element by constructing a chimeric lectin gene (/e7/Le7) that contained the 5' half of the /e7 gene and its promoter region and the 3' half of the wild-type Lel gene. Transformed tobacco seed containing the /el/Lel gene produced both lectin mRNA and protein, demonstrating that the mutant lectin gene control region is transcriptionally competent. By contrast, transformed seed containing the /e7 gene produced no detectable lectin mRNA. We conclude that the absence of detectable transcription from the /e7 gene is dueto transcriptional inhibition by the Tgml insertion element and that this element acts at a distance to block transcription from an upstream promoter region.