by John Collins — In the early 1960s, Werner Ar­ber in Switzer­land dis­cov­ered that for­eign DNA en­ter­ing a bac­te­r­ial cell could be cleaved on both strands by re­stric­tion en­donu­cle­ases (re­stric­tion en­zymes). This was part of the host's de­fense against vi­ral at­tack. For this dis­cov­ery he shared the 1978 No­bel Prize with Hamil­ton Smith and Daniel Nathans.