The BTB domain, also known as the POZ (poxvirus and zinc finger) domain, is an N-terminal homodimerization domain that contains multiple copies of kelch repeats and/or C2H2-type zinc fingers. Proteins that contain BTB domains are thought to be involved in transcriptional regulation via control of chromatin structure and function. RCBTB1 (regulator of chromosome condensation (RCC1) and BTB (POZ) domain containing protein 1), also known as GLP, CLLD7, CLLL7 or E4.5, is a 531 amino acid protein that localizes to the nucleus and contains two BTB (POZ) domains and six RCC1 repeats. Expressed ubiquitously, RCBTB1 is thought to be involved in cell cycle regulation, specifically via chromatin remodeling. The gene encoding RCBTB1 maps to a region on human chromosome 13 that is frequently deleted in B-cell chronic lymphocytic leukemia, suggesting a possible role for RCBTB1 in tumor suppression.