Cell Cycle Regulation

Ubiquitin is an abundant and essential cellular 9-kd protein that is conserved across evolution from yeast to humans. Ubiquitin is used by cells as a covalent modifier of other proteins both to activate their function and to target them for degradation, depending on the degree of ubiquitination.

Nucleolin is a ubiquitous, nonhistone nucleolar phosphoprotein of exponentially growing eukaryotic cells and is present in abundance at the dense fibrillar and granular regions of nucleolus. Intact nucleolin is the major species and represents 5% of nucleolar protein in actively dividing cells.

HA95 is a nuclear protein with high homology to the nuclear A-kinase anchoring protein AKAP95, involved in the regulation of nuclear envelope-chromatin interactions. Antibody immunostaining data indicate that HA95 is tightly associated with chromatin and the nuclear matrix/lamina network in interphase, and bound to chromatin at mitosis.

CDR2 is a tumor antigen expressed in a high percentage of breast and ovarian tumors and is the target of a naturally occurring tumor immune response in patients with paraneoplastic cerebellar degeneration.

Centromere protein F (CENPF), also named mitosin, is a large human protein of 3113 amino acid residues. Its expression and localization are cell cycle-dependent. The protein levels are low in G1 phase but elevated from S to early M phase. CENPF is a nuclear matrix protein in interphase but is relocated to the kinetochore, the major site of microtubule attachment on chromosome, in M phase (1).