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 arch
itecture. Our work has focused on transvection, a process that can cause ge
nes to be sensitive to the proximity of a homologue. Transvection is seen a
t the yellow gene of Drosophila, where it mediates numerous cases of intrag
enic 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 tran
scriptional competence. Our data suggest two ways in which transvection may
be regulated at yellow: (1) a transcriptional mechanism, whereby the abili
ty of an allele to support transvection is influenced by its transcriptiona
l competency, and (2) a structural mechanism, whereby the pairing of struct
urally dissimilar homologues results in conformational changes that affect
gene expression.