Order of authorship in the original publication: Linn, Arber. Arber announced the discovery, with proof, of the first restriction endonuclease (restriction enzyme or restrictase)."These enzymes are found in bacteria and archaea and provide a defence mechanism against invading viruses.^[4][5] Inside a prokaryote, the restriction enzymes selectively cut up foreign DNA in a process called restriction digestion; meanwhile, host DNA is protected by a modification enzyme (a methyltransferase) that modifies the prokaryotic DNA and blocks cleavage. Together, these two processes form the restriction modification system.^[6]"

Digital facsimile from PubMedCentral at this link.

(Thanks to Juan Weiss for this reference and its interpretation.)