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Science 17 December 1971:
Vol. 174. no. 4015, pp. 1200 - 1209
DOI: 10.1126/science.174.4015.1200
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Articles

Heterochromatin, Satellite DNA, and Cell Function

Jorge J. Yunis 1 and Walid G. Yasmineh 2

1 Department of laboratory medicine, University of Minnesota Medical School, Minneapolis 55455
2 Department of laboratory medicine, University of Minnesota Medical School

With the assumption that a portion that comprises some 10 percent of the genomes in higher organisms cannot be without a raison d'être, an extensive review led us to conclude that a certain amount of constitutive heterochromatin is essential in multicellular organisms at two levels of organization, chromosomal and nuclear. At the chromosomal level, constitutive heterochromatin is present around vital areas within the chromosomes. Around the centromeres, for example, heterochromatin is believed to confer protection and strength to the centromeric chromatin. Around secondary constrictions, heterochromatic blocks may ensure against evolutionary change of ribosomal cistrons by decreasing the frequency of crossing-over in these cistrons in meiosis and absorbing the effects of mutagenic agents. During meiosis heterochromatin may aid in the initial alignment of chromosomes prior to synapsis and may facilitate speciation by allowing chromosomal rearrangement and providing, through the species specificity of its DNA, barriers against cross-fertilization.

At the nuclear level of organization, constitutive heterochromatin may help maintain the proper spatial relationships necessary for the efficient operation of the cell through the stages of mitosis and meiosis. In the unicellular procaryotes, the presence of a small amount of genetic information in one chromosome obviates the need for constitutive heterochromatin and a nuclear membrane. At higher levels of organization, with an increase in the size of the genome and with evolution of cellular and sexual differentiation, the need for compartmentalization and structural components in the nucleus became imminent. The portion of the genome that was concerned with synthesis of ribosomal RNA was enlarged and localized in specific chromosomes, and the centromere became part of each chromosome when the mitotic spindle was developed in evolution. Concomitant with these changes in the genome, repetitive sequences in the form of constitutive heterochromatin appeared, probably as a result of large-scale duplication. The repetitive DNA's were kept through natural selection because of their importance in preserving these vital regions and in maintaining the structural and functional integrity of the nucleus.

The association of satellite (or highly repetitive) DNA with constitutive heterochromatin is understandable, since it stresses the importance of the structural rather than transcriptional roles of these entities. Nuclear satellite DNA's have one property in common despite their species specificity, namely heterochromatization. In this sense the apparent species specificity of satellite DNA may be the result of natural selection for duplicated short polynucleotide segments that are nontranscriptional and can be utilized in specific structural roles.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Recurrent Amplifications and Deletions of Satellite DNA Accompanied Chromosomal Diversification in South American Tuco-tucos (Genus Ctenomys, Rodentia: Octodontidae): A Phylogenetic Approach.
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Mol. Biol. Evol. 18, 1708-1719
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The origin of man: a chromosomal pictorial legacy.
J. Yunis and O Prakash (1982)
Science 215, 1525-1530
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The striking resemblance of high-resolution G-banded chromosomes of man and chimpanzee.
J. Yunis, Sawyer JR, and K Dunham (1980)
Science 208, 1145-1148
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Satellite DNA, H1 Histone, and Heterochromatin in Drosophila virilis.
M. Blumenfeld, J. W. Orf, B. J. Sina, R. A. Kreber, M. A. Callahan, and L. A. Snyder (1978)
Cold Spring Harb Symp Quant Biol 42, 273-276
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Quantitative Electron Microscopy of Chromosome Organization at Meiotic Prophase.
P. B. Moens (1974)
Cold Spring Harb Symp Quant Biol 38, 99-107
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The Evolution of Satellite DNA in Drosophila virilis.
M. Blumenfeld (1974)
Cold Spring Harb Symp Quant Biol 38, 423-427
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DNA Sequences Neighboring the Duck Hemoglobin Genes.
J. O. Bishop and K. B. Freeman (1974)
Cold Spring Harb Symp Quant Biol 38, 707-716
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Transcription and Chromatin Structure.
B. J. McCarthy, J. T. Nishiura, D. Doenecke, D. S. Nasser, and C. B. Johnson (1974)
Cold Spring Harb Symp Quant Biol 38, 763-771
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The Organization of Genetic Material in Eukaryotes: Progress and Prospects.
H. Swift (1974)
Cold Spring Harb Symp Quant Biol 38, 963-979
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Role of Heterochromatin in Homologous Chromosome Pairing: Evaluation of Evidence.
M. P. Maguire (1972)
Science 176, 543-544
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