HF stands for high fidelity. Many restriction endonucleases are capable of cleaving sequences which are similar but not identical to their defined recognition sequence. This altered or relaxed specificity has been termed star activity. HF restriction endonucleases have been engineered to cleave with higher fidelity than the wild type enzyme, hence exhibiting less star activity. Screens using increased glycerol concentration, increased reaction time and high enzyme concentration were used to identify enzymes that would offer the highest fidelity over a wide range of conditions. Learn more about High Fidelity Restriction Enzymes here .