EcoB and EcoK are type I enzymes, while HindII and HindIII are ... yielding what are known as blunt-end fragments (see Figure 3, in which PvuII similarly produces blunt-end fragments).

How, though, would a DNA-degrading enzyme distinguish between the two? Arber hypothesized that bacterial cells might express two types of enzymes ... enzymes produce "blunt" ends when they ...