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Biochem Cell Biol. 2009 Feb;87(1):229-41. doi: 10.1139/O08-119.

A lot about a little dot - lessons learned from Drosophila melanogaster chromosome 4.

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Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA.


The fourth chromosome of Drosophila melanogaster has a number of unique properties that make it a convenient model for the study of chromatin structure. Only 4.2 Mb overall, the 1.2 Mb distal arm of chromosome 4 seen in polytene chromosomes combines characteristics of heterochromatin and euchromatin. This domain has a repeat density of ~35%, comparable to some pericentric chromosome regions, while maintaining a gene density similar to that of the other euchromatic chromosome arms. Studies of position-effect variegation have revealed that heterochromatic and euchromatic domains are interspersed on chromosome 4, and both cytological and biochemical studies have demonstrated that chromosome 4 is associated with heterochromatic marks, such as heterochromatin protein 1 and histone 3 lysine 9 methylation. Chromosome 4 is also marked by POF (painting-of-fourth), a chromosome 4-specific chromosomal protein, and utilizes a dedicated histone methyltransferase, EGG. Studies of chromosome 4 have helped to shape our understanding of heterochromatin domains and their establishment and maintenance. In this review, we provide a synthesis of the work to date and an outlook to the future.

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