Position-effect variegation is the inactivation in some cells of a gene translocated next to heterochromatin, the region of the chromosome that is permanently condensed. The number of copies of the Drosophila gene Suvar(3)7 is a dose-limiting factor in this phenomenon, and seems from its sequence that it encodes a protein with five widely spaced zinc-fingers. This novel arrangement of zinc-fingers could help in packaging the chromatin fibre into heterochromatin, and also reflect a novel method of controlling the expression from DNA domains.