Role of Sic1 in The Cell Cycle Control
In the G1 phase of the cell cycle, Sic1 binds tightly to the Cdc28-Clb complex and inhibits it. Low Cdc28-Clb activity leads to the disassembly of the mitotic spindle, the assembly of the prereplicative complex and initiation of bud formation in yeast.
At the START point in the yeast cell cycle, the G1-cyclins Cln3, Cln1 and Cln 2 activate Cdc28. The activated complex will phosphorylate Sic1 at multiple sites which leads to its degradation by the SCF complex. When Sic1 is degraded, the Cdc28-Clb complex is no longer inhibited and the cell can enter the S/M-phase. Thus Sic1 inactivation is essential for transition into S phase (Fig.1).
Cdc28 in complex with B-type cyclin (Cdc28-Clb) phosphorylates Swi5, the transcription factor of Sic1. This promotes the export of Swi5 from the nucleus to the cytoplasm and avoids further transcription of the cdk inhibitor. Cdc28-Clb also phosphorylates any Sic1 molecules still available and triggers their ubiquitin-dependent degradation, exactly like Cdc28-Cln. High Cdc28-Clb levels also initiate DNA replication and duplication of the spindle pole bodies (SPBs). Then the metaphase spindle assembles and chromosome segregation can occur. The transcription of Sic1 starts during telophase, mediated by Swi5. Aca2 is another transcription factor of Sic1, but remains inactive until G1. At the end of mitosis, Sic1 is involved in the inactivation of Cdc28-Clb.
Read more about this topic: Sic1
Famous quotes containing the words role of, role, cell, cycle and/or control:
“To win by strategy is no less the role of a general than to win by arms.”
—Julius Caesar [Gaius Julius Caesar] (100–44 B.C.)
“Recent studies that have investigated maternal satisfaction have found this to be a better prediction of mother-child interaction than work status alone. More important for the overall quality of interaction with their children than simply whether the mother works or not, these studies suggest, is how satisfied the mother is with her role as worker or homemaker. Satisfied women are consistently more warm, involved, playful, stimulating and effective with their children than unsatisfied women.”
—Alison Clarke-Stewart (20th century)
“A cell for prayer, a hall for joy,—
They treated nature as they would.”
—Ralph Waldo Emerson (1803–1882)
“The Buddha, the Godhead, resides quite as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain or in the petals of a flower.”
—Robert M. Pirsig (b. 1928)
“We as a nation need to be reeducated about the necessary and sufficient conditions for making human beings human. We need to be reeducated not as parents—but as workers, neighbors, and friends; and as members of the organizations, committees, boards—and, especially, the informal networks that control our social institutions and thereby determine the conditions of life for our families and their children.”
—Urie Bronfenbrenner (b. 1917)