Restriction-Modification Enzymes

Discovery that bacteria defend against invading (phage) DNA by cutting it at specific sequences with a restriction endonuclease, while protecting their own DNA at the same sequence via methylation. Smith & Wilcox, "A restriction enzyme from Hemophilus influenzae. I. Purification and general properties" (J. Mol. Biol. 51, 379-391, 1970-07-01, OpenAlex W1506010125) reported the first isolation of a sequence-specific restriction enzyme (HindII), building on Werner Arber's 1960s prediction of restriction-modification systems. Smith shared the 1978 Nobel Prize in Physiology or Medicine with Arber and Daniel Nathans (who first applied restriction enzymes to map a genome, SV40, 1971). Directly enabled recombinant DNA / molecular cloning (Cohen, Boyer et al., 1973) -- the founding technology of the biotech industry -- not itself written as a separate node in this pass. Note: OpenAlex's author metadata for this record renders the second author as "K.W. Welcox"; the historically correct name is Kent W. Wilcox, used here.