Star activity is the relaxation or alteration of the specificity of
restriction enzyme
A restriction enzyme, restriction endonuclease, REase, ENase or'' restrictase '' is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class o ...
mediated cleavage of
DNA that can occur under reaction conditions that differ significantly from those optimal for the enzyme. The result is typically cleavage at non-canonical recognition sites, or sometimes complete loss of specificity.
Differences which can lead to star include low
ionic strength
The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds, when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such as ...
, high
pH, and high (> 5% v/v)
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
concentrations. The latter condition is of particular practical interest, since commercial restriction enzymes are usually supplied in a
buffer
Buffer may refer to:
Science
* Buffer gas, an inert or nonflammable gas
* Buffer solution, a solution used to prevent changes in pH
* Buffering agent, the weak acid or base in a buffer solution
* Lysis buffer, in cell biology
* Metal ion buffer
* ...
containing a substantial amount of glycerol (50% v/v is typical), meaning insufficient dilution of the enzyme solution can cause star activity; this problem most often arises during double or multiple digests.
Star activity can happen because of presence of Mg
2+, as is seen in
HindIII
''Hin''dIII (pronounced "Hin D Three") is a type II site-specific deoxyribonuclease restriction enzyme isolated from ''Haemophilus influenzae'' that cleaves the DNA palindromic sequence AAGCTT in the presence of the cofactor Mg2+ via hydrolysis ...
, for example.
The term star activity was introduced by Mayer
who characterized the modified activity in
EcoRI
''Eco''RI (pronounced "eco R one") is a restriction endonuclease enzyme isolated from species '' E. coli.'' It is a restriction enzyme that cleaves DNA double helices into fragments at specific sites, and is also a part of the restriction modific ...
.
External links
Star Activity-
New England Biolabs
New England Biolabs (NEB) produces and supplies recombinant and native enzyme reagents for the life science research, as well as providing products and services supporting genome editing, synthetic biology and next-generation sequencing. NEB also ...
Star Activity (Relaxation of Specificity)- Fermentas
Star activity of restriction enzymes- a detailed list from TaKaRa
*
References
Restriction enzymes
DNA
{{enzyme-stub