To the Editor.
——The article by the American Medical Association's Council on Scientific Affairs, "Biotechnology and the American Agricultural Industry,"1 discusses the safety of a range of genetically engineered food products now under development. The first example is of crop plants genetically engineered to resist insects by producing an insecticidal protein from the bacterium Bacillus thuringiensis (Bt). Unfortunately, the article's discussion of the safety of "Bt plants" as food is misleading in two ways.First, the article states that "Bt gene expression is generally limited to a single, highly susceptible developmental stage in the plant's life cycle (before maturation and harvest occur)." In most Bt plants developed so far, however, Bt genes are expressed throughout the plant; genetic engineers commonly control Bt gene expression with a promoter from cauliflower mosaic virus that keeps genes "turned on." A number of investigators are now experimenting with other promoters that target gene