Abstract
The Drosophila bric à brac protein and the transcriptional regulators encoded by tramtrack and Broad-Complex contain a highly conserved domain of approximately 115 amino acids, which we have called the BTB domain. We have identified six additional Drosophila genes that encode this domain. Five of these genes are developmentally regulated, and one of them appears to be functionally related to bric à brac. The BTB domain defines a gene family with an estimated 40 members in Drosophila. This domain is found primarily at the N terminus of zinc finger proteins and is evolutionarily conserved from Drosophila to mammals.