WHITE GENE-EXPRESSION, REPRESSIVE CHROMATIN DOMAINS AND HOMEOTIC GENE-REGULATION IN DROSOPHILA

The use of Drosophila chromosomal rearrangements and transposon constr ucts involving the white gene reveals the existence of repressive chro matin domains that can spread over considerable genomic distances. One such type of domain is found in heterochromatin and is responsible fo r classical position-effect variegation. Another type of repressive do main is established, beginning at specific sequences, by complexes of Polycomb Group proteins. Such complexes, which normally regulate the e xpression of many genes, including the homeotic loci, are responsible for silencing, white gene variegation, pairing-dependent effects and i nsertional targeting.