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Published December 1, 1982 | Published
Journal Article Open

Protein D1 preferentially binds A+T-rich DNA in vitro and is a component of Drosophila melanogaster nucleosomes containing A+T-rich satellite DNA


Our previous work [Levinger, L. & Varshavsky, A. (1982) Cell 28, 375-385] has shown that D1, a 50-kilodalton chromosomal protein of Drosophila melanogaster, is specifically associated with isolated nucleosomes that contain a complex A+T-rich satellite DNA with buoyant density of 1.688 g/ml. We show here that D1 is also a component of nucleosomes containing a simple-sequence, pure A+T satellite DNA, buoyant density 1.672 g/ml. Furthermore, using a modification of a protein blotting technique in which proteins are not exposed to dodecyl sulfate denaturation, we have found that D1 preferentially binds to A+T-rich double-stranded DNA in vitro, and it is apparently the only abundant nuclear protein in cultured D. melanogaster cells that possesses this property. Synthetic poly[(A-T)]· poly[d(A-T)] and poly(dA)· poly(dT) duplexes effectively compete in vitro with A+T-rich D. melanogaster satellite DNAs for binding to D1, whereas total Escherichia coli DNA is an extremely poor competitor. These findings strongly suggest that D1 is a specific component of A+T-rich, tandemly repeated, heterochromatic regions, which constitute up to 15-20% of the total D. melanogaster genome. Possible functions of D1 protein include compaction of A+T-rich heterochromatin and participation in microtubule--centromere interactions in mitosis. In addition, D1 may prevent nonspecific binding to A+T-rich satellite DNA of other nuclear proteins that have a preference for AT-DNA, such as RNA polymerase or regulatory proteins, and may also participate in the higher-order chromatin organization outside tandemly repetitive regions by binding to nonrandomly positioned stretches of A+T-rich DNA.

Additional Information

© 1982 by the National Academy of Sciences. Communicated by Paul Doty, August 25, 1982. We are grateful to Douglas Brutlag for providing us with satellite DNA clones. This work was supported by grants to A.V. from the National Cancer Institute and the National Institute of General Medical Sciences. L. L. was supported by a postdoctoral fellowship from the Medical Foundation. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

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