This family includes ORF A55R from Vaccinia virus, which is characterised by having a BTB (for BR-C, ttk and bab) []or POZ (for Pox virus and Zinc finger) []domain near the N terminus. The proteins are also characterised by kelch repeats C-terminal to the BTB domain. The function of these proteins are unknown.
The BTB (for BR-C, ttk and bab) []or POZ (for Pox virus and Zinc finger) [, ]domain is a versatile protein-protein interaction motif involved in many cellular functions, including transcriptional regulation, cytoskeleton dynamics, ion channel assembly and gating, and targeting proteins for ubiquitination []. The BTB domain can occur alongside other domains: BTB-zinc finger (BTB-ZF), BTB-BACK-Kelch (BBK), voltage-gated potassium channel T1 (T1-Kv) [], MATH-BTB, BTB-NPH3 and BTB-BACK-PHR (BBP). Other proteins, such as Skp1 and ElonginC, consist almost exclusively of the core BTB fold. In all of these protein families, the BTB core fold is structurally conserved, consisting of a 2-layer alpha/beta topology where a cluster of alpha helices is flanked by short β-sheets []. POZ domains from several zinc finger proteins have been shown to mediate transcriptional repression and to interact with components of histone deacetylase co-repressor complexes including N-CoR and SMRT [, , ]. The POZ or BTB domain is also known as BR-C/Ttk or ZiN.This entry includes the BTB/POZ domain, as well as Skp1 N-terminal region which has an α/β structure similar to that of the BTB/POZ domain fold [, ].
