Mixed with EcoRI-treated plasmid and DNA ligase, a small number of the human molecules will become incorporated into the plasmid which can then be used to transform E. coli. The key is that the EcoRI site is within the kan r gene, so when a piece of human DNA is inserted there, the gene's function is destroyed. All E. coli cells transformed by the vector, whether it carries human DNA or not, can grow in the presence of ampicillin. But E. coli cells transformed by a plasmid carrying human DNA will be unable to grow in the presence of kanamycin. Some recombinant DNA products being used in human therapy Using procedures like this, many human genes have been cloned in E. coli or in yeast.
Many more examples are in the pipeline.