What is star activity in a restriction enzyme?

Correct answer: Cutting at similar sites besides the normal site

Direct answer: option D, cutting at sites similar to the normal recognition site. Restriction enzymes usually recognise a particular DNA sequence and cut it specifically. Under unsuitable reaction conditions, their specificity can decrease; the enzyme may then cut at sequences that resemble, but are not exactly, the normal site. This unusual relaxed specificity is called star activity. Option A, enzyme storage only, describes handling and has nothing to do with altered DNA recognition. Option B, DNA ligation only, means joining DNA fragments and is a different enzymatic process. Option C, protein staining only, concerns visualising proteins, not restriction digestion. Option D correctly describes extra cutting at similar sites. Star activity can be encouraged by too much enzyme, excessive reaction time, unsuitable buffer or other non-ideal conditions. In careful experiments, use the recommended buffer, enzyme amount and incubation time. Memory cue: star activity means the restriction enzyme becomes less strict about its target sequence.