A new family of genes which, when mutated, suppress the inhibitory effect of the mod(mdg4)1u1 mutation on y2 expression in Drosophila melanogaster

EAST affects the activity of Su(Hw) insulators by two different mechanisms in Drosophila melanogaster

Recent data suggest that insulators organize chromatin architecture in the nucleus. The best characterized Drosophila insulator, found in the gypsy retrotransposon, contains 12 binding sites for the Su(Hw) protein. Enhancer blocking, along with Su(Hw), requires BTB/POZ domain proteins, Mod(mdg4)-67.2 and CP190. Inactivation of Mod(mdg4)-67.2 leads to a direct repression of the yellow gene promoter by the gypsy insulator. Here, we have shown that such repression is regulated by the level of the EAST protein, which is an essential component of the interchromatin compartment. Deletion of the EAST C-terminal domain suppresses Su(Hw)-mediated repression. Partial inactivation of EAST by mutations in the east gene suppresses the enhancer-blocking activity of the gypsy insulator. The binding of insulator proteins to chromatin is highly sensitive to the level of EAST expression. These results suggest that EAST, one of the main components of the interchromatin compartment, can regulate the activity of chromatin insulators.

An analysis of transvection at the yellow locus of Drosophila melanogaster

Studies of a wide variety of organisms have shown that homologous sequences can exert a significant impact on each other, resulting in changes in gene sequence, gene expression, chromatin structure, and global chromosome architecture. Our work has focused on transvection, a process that can cause genes to be sensitive to the proximity of a homologue. Transvection is seen at the yellow gene of Drosophila, where it mediates numerous cases of intragenic complementation. In this article, we describe two approaches that have characterized the process of transvection at yellow. The first entailed a screen for mutations that support intragenic complementation at yellow. The second involved the analysis of 53 yellow alleles, obtained from a variety of sources, with respect to complementation, molecular structure, and transcriptional competence. Our data suggest two ways in which transvection may be regulated at yellow: (1) a transcriptional mechanism, whereby the ability of an allele to support transvection is influenced by its transcriptional competency, and (2) a structural mechanism, whereby the pairing of structurally dissimilar homologues results in conformational changes that affect gene expression.