These are also designed for invasiveness, to overcome mechanisms that guard against their integration and expression in foreign genomes. They range from oligonucleotides to artificial constructs thousands and millions of basepairs in length, often containing heterogeneous arrays of genes from pathogenic bacteria, viruses and other genetic parasites belonging to every kingdom of living organisms. Some gene therapy vectors and vaccines have already been found to elicit toxic and other harmful reactions. Nucleic acids are now known to persist in all environments, including the digestive tract. Transformation by the uptake of DNA is a significant route of horizontal gene transfer, and there is overwhelming evidence that horizontal gene transfer and recombination have been responsible for the recent resurgence of drug and antibiotic resistant infectious diseases.
Integration can result in harmful biological effects, including cancers.
There is also the potential for generating new viruses by horizontal gene transfer and recombination. In short, the need to establish regulatory oversight of such artificial constructs at both national and international levels is long overdue. Promoters are gene switches for turning genes on, and every functioning gene has to have one. Promoters typically have a modular construction, consisting of parts that respond to different signals from a battery of other genes, which determine where and when they are turned on, by how much and for how long. Thus, promoters allow genes to talk to one another.