Some data suggests that salt concentrations greater than 10 mM may inhibit HpaI activity. (Krotee, S., unpublished observation) Therefore, mini prep DNA containing residual salt can be resistant to HpaI cleavage. A 70% ethanol wash or dialysis is recommended to remove the salt. When performing ethanol precipitations, potassium acetate is recommended if necessary rather than ammonium acetate or sodium acetate due to possible inhibition of HpaI activity.