The concept that there exist functional networks of genes which program early development, and that genes which encode proteins with multiple conserved domains serve to cross-link such networks. Thus, a set of genes containing domain A and a set containing domain B are linked by genes containing both domains. The segmentation gene paired (prd) of Drososphila illustrates the theory. It contains a homeobox (q.v.) and a histidine-proline repeat domain. This prd-specific repeat occurs in at least 12 other genes, while the homeobox defines a second gene set. Presumably, the prd product can interact with products of genes containing only the homeobox sequence or the histidine-proline repeat, or both. The conserved domains are thought to serve as the sites to which the proteins bind to specific chromosomal regions to regulate neighboring genes. See Chronology, 1986, Noll et al.; eyeless.
Subjects: Genetics and Genomics.