Effects of chromosomal rearrangements on transvection at the yellow gene of Drosophila melanogaster.

Homologous chromosomes are paired in somatic cells of Drosophila melanogaster. This pairing can lead to transvection, which is a process by which the proximity of homologous genes can lead to a change in gene expression. At the yellow gene, transvection is the basis for several examples of intragenic complementation involving the enhancers of one allele acting in trans on the promoter of a paired second allele. Using complementation as our assay, we explored the chromosomal requirements for pairing and transvection at yellow. Following a protocol established by Ed Lewis, we generated and characterized chromosomal rearrangements to define a region in cis to yellow that must remain intact for complementation to occur. Our data indicate that homolog pairing at yellow is efficient, as complementation was disrupted only in the presence of chromosomal rearrangements that break<or=650 kbp from yellow. We also found that three telomerically placed chromosomal duplications, containing approximately 700 or more kbp of the yellow genomic region, are able to alter complementation at yellow, presumably through competitive pairing interactions. These results provide a formal demonstration of the pairing-dependent nature of yellow transvection and suggest that yellow pairing, as measured by transvection, reflects the extent of contiguous homology flanking the locus.