An investigation of heterochromatin domains on the fourth chromosome of Drosophila melanogaster

The banded portion of the fourth chromosome of Drosophila melanogaster exhibits characteristics of euchromatin and heterochromatin. Reminiscent of heterochromatin, it contains a high percentage of repetitive elements, does not undergo recombination, and exhibits high levels of HP1 and histone 3 lysine 9 dimethylation. However, in the distal 1.2Mb, the gene density is typical of euchromatin, and this region is polytene in salivary gland nuclei. Using P element reporters carrying a copy of hsp70-white, alternative chromatin packaging domains can be distinguished by the eye color phenotype. Mapping studies identified the repetitive element 1360 as a candidate for heterochromatin targeting in the fourth chromosome Hcf region. We report here two new screens using this reported to look for additional heterochromatin target sites. We confirm that reporter elements within 10kb of 1360 are usually packaged as heterochromatin; however, heterochromatin packaging occurs in the sv region in the absence of 1360. Analyses of the sequences adjacent to P element reporters show no simple association between specific repeated elements and transgene expression phenotype on a whole chromosome level. The data require that heterochromatin formation as a whole depends on a more complex pattern of sequence organization rather than the presence of a single particular sequence element.

Key Words: Drosophila, dot chromosome, genome organization, heterochromatin, repetitious elements

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
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