Allelic pairing and gene regulation: A model for the zeste—white interaction in Drosophila melanogaster

Abstract
The z locus of D. melanogaster apparently represses locus activity, but the repression is effective only on paired or physically adjacent w loci. Various mutant alleles of z and w were combined in a series of different doses to determine the effect of dosage and physical position in the nucleus on gene expression. In z/z individuals, paired white alleles failed to be expressed, while unpaired alleles were expressed normally. A model postulating that the z gene product represses the transcription of w+ by complexing with an RNA produced by part of the white locus itself is advanced. To be effective in repression, there must be 2 w+ genes producing the RNA in a limited volume in the nucleus. Such a model necessarily imposes a specific architecture on the chromatin of interphase nuclei.