BTB (also known as POZ) was first identified as a conserved motif presented in the Drosophila melanogaster Bric-a-Brac, Tramtrack, Broad complex transcription regulators (1). BTB, Cul3 and RBX1 form a Cul3-based ligase (BCR), which targets substrates for ubiquitin-dependent degradation by the 26S proteasome. As a substrate recognition subunit of Cul3-based ligase, the member of BTB family can bridge the Cul3 to the substrate in a single polypeptide (2,3). Recently, it was observed that a 3-box is responsible for the Cul3-interacting in a variety of BTB proteins including almost all of BTB-Kelch and MATH-BTB proteins (4). Here we defined the BTB_Other family as the proteins contain only BTB domain but not 3-box domain. BTB-containing proteins are highly conserved and participate in diverse biological processes, including transcriptional regulation, ion channel assembly and gating, cytoskeleton dynamics, and targeting proteins for ubiquitination (1).
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