Acknowledgments This paper is dedicated, on the occasion of her 100th birthday, to Rita Levi- Montalcini who discovered that neuron death (later called apoptosis) could occur during development of chicken embryos (see Levi-Montalcini and Levi, Arch. Biol 53, 537–545, 1942). We wish to thank our colleagues Oliver Clay for very helpful comments, Fabio Auletta and Giuseppe Torelli for their help in computer work ,and References 1. Felsenfeld G, Groudine M (2003) Controlling the double helix. Nature 421: 448–453. 2. Kornberg RD, Lorch Y (2007) Chromatin rules. Nat Struct Mol Biol 14: 986–988. 3. Hewish DR, Burgoyne LA (1973) Chromatin sub-structure. The digestion of chromatin DNA at regularly spaced sites by a nuclear deoxyribonuclease. Biochem Biophys Res Commun 52: 504–510. 4. Kerr JFR, Wyllie AH, Currie AR (1972) Apoptosis: a basic biological phenomenon with wide-ranging implication in tissue kinetics. Brit J Cancer 68: 239–257. 5. Steller H (1995) Mechanisms and genes of cellular suicide. Science 267: 1445–1449. 6. Wyllie A (1980) Glucocorticoid-induced thymocyte apoptosis is associated with endogenous endonuclease activation. Nature 284: 555–556. 7. Counis MF, Torriglia A (2000) DNases and apoptosis. Biochem Cell Biol 78: 405–414. 8. Scovassi AI, Torriglia A (2003) Activation of DNA-degrading enzymes during apoptosis. Eur J of Histochem 47: 185–19. 9. Counis MF, Torriglia A (2006) Acid DNases and their interest among apoptotic endonucleases. Biochimie 88: 1851–1858. 10. Filipski J, Leblanc J, Youdale T, Sikorska M, Walker PR (1990) Periodicity of DNA folding in higher order chromatin structure. EMBO J 9: 1319–1327. 11. Walker PR, Sikorska M (1997) New aspects of the mechanism of DNA fragmentation in apoptosis. Biochem Cell Biol 75: 287–299. 12. Hale AJ, et al. (1996) Apoptosis: molecular regulation of cell death. Eur J Biochem 236: 1–26. 13. Compton MM (1992) A biochemical hallmark of apoptosis: internucleosomal degradation of the genome. Cancer Metastasis Rev 11: 105–119. 14. Costantini M, Di Filippo M, Auletta F, Bernardi G (2007) Isochore pattern and gene distribution in the chicken genome. Gene 400: 9–15. 15. Olofsson B, Bernardi G (1983) The distribution of CR1, and Alu-like family of interspersed repeats, in the chicken genome. Biochim Biophys Acta 740: 339–341. 16. Coullin P, Bed’Hom B, Candelier JJ, Vettese D, Maucolin S, et al. (2005) Cytogenetic repartition of chicken CR1 sequences evidenced by PRINS in Galliformes and some other birds. Chromosome Res 13: 675–673. Apoptotic Attack on Chromatin the Molecular Biology Service of the Stazione Zoologica Anton Dohrn for the clone sequencing. Author Contributions Conceived and designed the experiments: GB. Performed the experiments: MDF. Analyzed the data: MDF GB. Wrote the paper: MDF GB. 17. Horz W, Haltenburger W (1981) Sequence specific cleavage of DNA by micrococcal nuclease. Nucleic Acid Res 9: 2643–2658. 18. Dingwall C, Lomonossoff GP, Laskey RA (1981) High sequence specificity of micrococcal nuclease. Nucleic Acids Res 9: 2659–2673. 19. Cockell M, Rhodes D, Klug A (1983) Location of the primary sites of micrococcal nuclease cleavage on the nucleosome core. J Mol Biol 170: 423–446. 20. Flick JT, Eissenberg JC, Elgin SC (1986) Micrococcal nuclease as a DNA structural probe: its recognition sequences, their genomic distribution and correlation with DNA structure determinants. J Mol Biol 190: 619–633. 21. Fox KR (1992) Wrapping of genomic poly dApoly dT tracts around nucleosome core particles. Nucleic Acids Res 20: 1235–1242. 22. Widlak P, Garrard WT (2006) Unique features of the apoptotic endonuclease DFF40/CAD relative to micrococcal nuclease as a structural probe for chromatin. Biochemistry and Cell Biology 84: 405–410. 23. Saccone S, Federico C, Bernardi G (2002) Localization of the gene-richest and the gene-poorest isochores in interphase nuclei of mammals and birds. Gene 300: 169–178. 24. Bernardi G (2004) Structural and Evolutionary Genomics. Natural Selection in Genome Evolution. The Netherland: Elsevier reprinted in 2005. 25. Bernardi G (2007) The neoselectionist theory of genome evolution. Proc Natl Acad Sci U S A 104: 8385–8390. 26. Di Filippo M, Bernardi G (2008) Mapping DNase-I hypersensitive sites on human isochores. Gene 419: 62–65. 27. Hughes FM, Evans-Storms RB, Cidlowski JA (1998) Evidence that non-caspase proteases are required for chromatin degradation during apoptosis. Cell Death Differ 5: 1017–1027. 28. Counis MF, Torriglia A (2006) Acid DNases and their interest among apoptotic endonucleases. Biochimie 88: 1851–1858. 29. Kornberg RD, LaPointe JW, Lorch Y (1989) Preparation of nucleosomes and chromatin. Methods Enzymol 170: 3–14. 30. Varriale A, Bernardi G (2006) DNA methylation and body temperature in fishes. Gene 385: 111–121. PLoS ONE | www.plosone.org 7 April 2009 | Volume 4 | Issue 4 | e5010