BTB sequence clusters and protein architectures. Family-specific amino- and carboxy-terminal extensions to the core BTB fold are indicated. Regions with no predicted secondary structure are indicated by dashed lines, and ordered regions are indicated with either domain notations or thick solid lines. The Uniprot code for a representative protein is indicated. Clustering by BLASTCLUST was based on the average pairwise sequence identity for all BTB domain sequences from our database, except for the RhoBTB proteins, where only the carboxy-terminal BTB domain was used. Domain names are from Pfam .