A characteristic feature of apoptosis is activation of an endonuclease(s), which has preference for internucleosomal DNA (reviewed in 1 –5 ). As a result, the products of DNA cleavage during apoptosis are discontinuous DNA sections of mono- and oligonucleosome size, which generate a typical “ladder” pattern during gel electrophoresis. This electrophoretic pattern is considered to be a hallmark of apoptosis (1 –5 ). Although exceptions to this pattern have been observed (6 –10 ), analysis of DNA size on agarose gels is a widely used procedure to reveal apoptosis. Generally, DNA for gel electrophoresis is extracted with phenol or recovered using other standard isolation procedures.
