Editing Star Activity

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´)

EcoRI, the rate difference between cognate and star sites approaches zero as ethylene glycol concentration increases up to 4M

EcoRV, the rate difference drops to only sixfold when Mn2+ is substituted for Mg2+ (2) .

The following has star activity AvaI BamHI BanI BmeI BmrI BspLUIII BstI BsuRI BtsI CeqI CviJI EcoRI EcoRV HaeIII HhaI HindIII HinfI KpnI MamI MboII NcuI NotI PpiI PstI PvuII RsrI SacI SalI SauAI SgrAI SphI SstI TaqI TthI, XbaI

Experimentally, it has been found that the following general conditions may increase star activity: high glycerol concentration (>5% v/v) (18–20,34), high enzyme to DNA ratio (usually >100U of enzyme per microgram of DNA) (12,17,20,34), low ionic strength (&lt;25mM salt) (12,17,20,34,35), high pH (&gt;8.0) (41), the presence of organic solvents (such as DMSO, ethanol) (20,34,43) and substitution of Mg2+ with other divalent cations (Mn2+, Co2+)

EcoRI cleaves 50-GAATTC-30under normal conditions, and is reported to cleave 50NAATTN-30 under star conditions (12,68); when used under star conditions, EcoRI behaves like an enzyme that recognizes any 50AATT-30 sequence, which is the same as the newer enzyme Tsp509I
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