CCNB1 (cyclin B1)

Abstract

IdentityOther names: CCNB HGNC (Hugo): CCNB1 Location: 5q13.2 DNA/RNA Description 9 exons; 2,087 bp; 433 residues CCNB1 transcript 1. 8 exons; 1,833 bp; 397 residues CCNB1 transcript 2. TranscriptionTwo alternative transcripts resulting from distinct transcription initiation sites. One is constitutively expressed and the other is G2/M cell cycle-regulated. PseudogeneNo verified pseudogenes. Protein DescriptionCyclin B1 (48.337 kDa) is a member of the cyclin family of proteins whose levels vary during the cell cycle in order to activate specific cyclin-dependent kinases (CDKs) required for the proper progression through the cell cycle. Cyclin B1 protein begins to increase during G2, peaks in mitosis, and is rapidly degraded before the cell cycle is completed. Cyclin B1 interacts with CDK1 to form a complex known as the maturation-promoting factor (MPF), which is essential for cell cycle progression through mitosis. When chromosomes are properly aligned during anaphase, rapid degradation of cyclin B1 by anaphase-promoting complex/cyclosome (APC/C) is required for mitotic exit and completion of the cell cycle. ExpressionCyclin B1 is overexpressed in a variety of cancers compared to normal cells and tissues. In normal tissues, low levels of cyclin B1 is detected in testis, thymus, bone marrow, and smooth muscle (CCNB1 expression). In most primary tumors, the expression of cyclin B1 is "unscheduled" (unrestricted to particular phases of the cycle), whereas in normal lymphocytes, the expression of cyclin B1 is restricted to very late S and G2 + M phases of the cell cycle (Gorczyca et al., 1997). LocalisationDuring interphase, cyclin B1 is concentrated in the cytoplasm but can shuttle to the nucleus (Pines and Hunter, 1991).Diagram of sequence domains for cyclin B1. The destruction box (DB) is required for degradation of cyclin B1 at the metaphase-toanaphase transition. The cytoplasmic retention sequence (CRS) and the nuclear export signal (NES) are critical determinants of cyclin B1 localization during mitosis. The cyclin box is required for interaction with CDK1.