DNA fragmentation during apoptosis is caused by frequent single-strand cuts.
One of the hallmarks of apoptosis is the digestion of genomic DNA by an endonuclease, generating a ladder of small fragments of double-stranded DNA. We have examined the nature of the DNA breaks produced in mouse thymocytes triggered to undergo apoptosis by steroids or by stimulation of the T cell receptor. Whereas the typical ladder pattern of oligonucleosomal fragments was observed after agarose gel electrophoresis, numerous single-strand cuts were detected after electrophoresis under denaturing conditions. Single-strand nicks were found to be very frequent in the internucleosomal regions, but also to occur in the core particle-associated DNA. An identical pattern of single-strand nicks was obtained when chromatin DNA was exposed to the single-strand cleaving deoxyribonuclease I. The nicked DNA fragments, extracted from apoptotic thymocytes, were sensitive to the action of S1-nuclease. We propose that DNA fragmentation induced during apoptosis is not due to a double-strand cutting enzyme as previously postulated, but rather is the result of single-strand breaks. This ensures the dissociation of the DNA molecule at sites where cuts are found within close proximity.
Peitsch
M C
MC
Institute of Biochemistry, University of Lausanne, Epalinges, Switzerland.
Müller
C
C
Tschopp
J
J
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D017252:CD3 Complex / Q000502:physiology; D002478:Cells, Cultured; D003198:Computer Simulation; D004249:DNA Damage; D003907:Dexamethasone / Q000494:pharmacology; D004587:Electrophoresis, Agar Gel; D051379:Mice; D015398:Signal Transduction
D017252:CD3 Complex; D003907:Dexamethasone