High-resolution analysis of Drosophila heterochromatin organization using SuUR Su(var)3-9 double mutants.

The structural and functional analyses of heterochromatin are essential to understanding how heterochromatic genes are regulated and how centromeric chromatin is formed. Because the repetitive nature of heterochromatin hampers its genome analysis, new approaches need to be developed. Here, we describe how, in double mutants for Su(var)3-9 and SuUR genes encoding two structural proteins of heterochromatin, new banded heterochromatic segments appear in all polytene chromosomes due to the strong suppression of under-replication in pericentric regions.

The SU(VAR)3-9/HP1 complex differentially regulates the compaction state and degree of underreplication of X chromosome pericentric heterochromatin in Drosophila melanogaster.

In polytene chromosomes of Drosophila melanogaster, regions of pericentric heterochromatin coalesce to form a compact chromocenter and are highly underreplicated. Focusing on study of X chromosome heterochromatin, we demonstrate that loss of either SU(VAR)3-9 histone methyltransferase activity or HP1 protein differentially affects the compaction of different pericentric regions. Using a set of inversions breaking X chromosome heterochromatin in the background of the Su(var)3-9 mutations, we show that distal heterochromatin (blocks h26-h29) is the only one within the chromocenter to form a big "puff"-like structure.

Two distinct domains in Drosophila melanogaster telomeres.

Telomeres are generally considered heterochromatic. On the basis of DNA composition, the telomeric region of Drosophila melanogaster contains two distinct subdomains: a subtelomeric region of repetitive DNA, termed TAS, and a terminal array of retrotransposons, which perform the elongation function instead of telomerase. We have identified several P-element insertions into this retrotransposon array and compared expression levels of transgenes with similar integrations into TAS and euchromatic regions.