In 1950, Luria moved to the University of Illinois at Urbana–Champaign. In the early 1950s, Luria and Giuseppe Bertani discovered the phenomenon of host-controlled restriction and modification of a bacterial virus: a culture of "E. coli" can significantly reduce the production of phages grown in other strains; however, once the phage become established in that strain, they also become restricted in their ability to grow in other strains. It was later discovered by other researchers that bacteria produce enzymes that cut viral DNA at particular sequences but not the bacteria's own DNA, which is protected by methylation. These enzymes became known as restriction enzymes and developed into one of the main molecular tools in molecular biology.