BIOLOGICAL PROPERTIES OF A HEMOPHILUS-INFLUENZAE RESTRICTION ENZYME, HIND-1

A type I restriction enzyme from H. influenzae, Hind I, which requires ATP and 5-adenosyl methionine, was studied for its activity on transfecting and transforming DNA. The enzyme reduced the size of unmodified bacteriophage S2 DNA from 37 .times. 106 to .apprx. 10 .times. 106 daltons, but did not affect modified S2 DNA. Unmodified transforming DNA was attacked in vitro by Hind I; relatively low levels of inactivation were obtained for single markers, and linked transformants were inactivated as a function of the distance between markers. Unmodified bacterial DNA [from H. influenzae and H. parainfluenzae] was not inactivated in vivo for single or linked markers by the Hind I restriction system, probably because the segments generated by Hind I were still capable of being integrated in vivo. The lack of preferential inactivation of markers by the enzyme suggests that it makes random breaks in the DNA.