XB-ART-17750Mol Biol Cell September 1, 1996; 7 (9): 1343-57.
Mutagenic analysis of the destruction signal of mitotic cyclins and structural characterization of ubiquitinated intermediates.
Mitotic cyclins are abruptly degraded at the end of mitosis by a cell-cycle-regulated ubiquitin-dependent proteolytic system. To understand how cyclin is recognized for ubiquitin conjugation, we have performed a mutagenic analysis of the destruction signal of mitotic cyclins. We demonstrate that an N-terminal cyclin B segment as short as 27 residues, containing the 9-amino-acid destruction box, is sufficient to destabilize a heterologous protein in mitotic Xenopus extracts. Each of the three highly conserved residues of the cyclin B destruction box is essential for ubiquitination and subsequent degradation. Although an intact destruction box is essential for the degradation of both A- and B-type cyclins, we find that the Xenopus cyclin A1 destruction box cannot functionally substitute for its B-type counterpart, because it does not contain the highly conserved asparagine necessary for cyclin B proteolysis. Physical analysis of ubiquitinated cyclin B intermediates demonstrates that multiple lysine residues function as ubiquitin acceptor sites, and mutagenic studies indicate that no single lysine residue is essential for cyclin B degradation. This study defines the key residues of the destruction box that target cyclin for ubiquitination and suggests there are important differences in the way in which A- and B-type cyclins are recognized by the cyclin ubiquitination machinery.
PubMed ID: 8885231
PMC ID: PMC275986
Article link: Mol Biol Cell
Genes referenced: ccna1 ccnb1.2
References [+] :
Amon, Closing the cell cycle circle in yeast: G2 cyclin proteolysis initiated at mitosis persists until the activation of G1 cyclins in the next cycle. 1994, Pubmed