We believe this site might serve you best:

United States

English Continue

This country code will remain if no action is taken to change it.

Don't see your country?
Promega Corporation

What is restriction enzyme star activity?


Related Products

  • Print
  • Email
  • Download PDF

The precise specificity of the approximately 3,000 known restriction enzymes for their >200 different target sequences could be considered their most interesting characteristic. Although all restriction enzymes bind DNA nonspecifically, under optimal conditions the difference in cleavage rates at the cognate site and the next best site (single-base substitution) is very high. For example, the rate difference for EcoRI at its cognate site (5´-GAATTC-3´) and next best site (5´-TAATTC-3´) is of the order of 105 (1) . Similarly, for EcoRV, cleavage at its cognate site (5´-GATATC-3´) is 106 times faster than at the next best site (5´-GTTATC-3´) (2) .

However, under nonoptimal conditions, the differences in cleavage rates between cognate and next-best sites change dramatically for many enzymes. This loss of fidelity or increase in cleavage at sites similar to the cognate site is commonly referred to as star activity. A number of reaction parameters can increase the rate of cleavage at star sites relative to cognate sites. These include pH, type of ions present, ionic strength, metal cofactors other than Mg2+, high enzyme:DNA ratios and the presence of volume excluders (glycerol, ethylene glycol, etc.). In conjunction with this increase in star activity, cleavage rates at the cognate site generally decrease. For example, for EcoRI, the rate difference between cognate and star sites approaches zero as ethylene glycol concentration increases up to 4M (3) , and for EcoRV, the rate difference drops to only sixfold when Mn2+ is substituted for Mg2+ (2) .

For more information on the proposed mechanisms for star activity and a list of enzymes that exhibit star activity, see the Restriction Enzymes Resource.


  1. Lesser, D.R., Kurpiewski, M.R. and Jen-Jacobson, L. (1990) The energetic basis of specificity in the EcoRI endonuclease--DNA interaction. Science 250, 776–86.
  2. Vermote, C.L. and Halford, S.E. (1992) EcoR V restriction endonuclease: Communication between catalytic metal ions and DNA recognition. Biochemistry 31, 6082–9.
  3. Robinson, C.R. and Sligar, S.G. (1998) Changes in solvation during DNA binding and cleavage are critical to altered specificity of the EcoRI endonuclease. Proc. Natl. Acad. Sci. USA 95, 2186–91.

Products may be covered by pending or issued patents or may have certain limitations. Please visit our Web site for more information.

It appears that you have Javascript disabled. Our website requires Javascript to function correctly. For the best browsing experience, please enable Javascript.

Scientists at Your Service

Scientists at Your Service

We offer a range of services to help you succeed using Promega technologies. From product training to set up of automated systems and development of custom applications—our scientific support goes beyond the basics.

Ask us! We are here to help you.