After decades of work, Dr. Ricky M. isolated a small amount of attractase an enzyme that produces a powerful human pheromone from hair samples of Hollywood celebrities. To take advantage of attractase for his personal use, he obtained a complete genomic clone of the attractase gene, connected it to a strong bacterial promoter on an expression plasmid, and introduced the plasmid into E. coli cells. He was devastated to find that no attractase was produced in the cells. What is a likely explanation for his failure?