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:
“Scholars who become politicians are usually assigned the comic role of having to be the good conscience of state policy.”
—Friedrich Nietzsche (1844–1900)
“American feminists have generally stressed the ways in which men and women should be equal and have therefore tried to put aside differences.... Social feminists [in Europe] ... believe that men and society at large should provide systematic support to women in recognition of their dual role as mothers and workers.”
—Sylvia Ann Hewitt (20th century)
“Women have no wilderness in them,
They are provident instead,
Content in the tight hot cell of their hearts
To eat dusty bread.”
—Louise Bogan (1897–1970)
“The cycle of the machine is now coming to an end. Man has learned much in the hard discipline and the shrewd, unflinching grasp of practical possibilities that the machine has provided in the last three centuries: but we can no more continue to live in the world of the machine than we could live successfully on the barren surface of the moon.”
—Lewis Mumford (1895–1990)
“... the black girls didn’t get these pills because their black ministers were up on the pulpit saying that birth control pills were black genocide. What I’m saying is that black men have exploited black women.... They didn’t want them to have any choice about their reproductive health. And if you can’t control your reproduction, you can’t control your life.”
—Joycelyn Elders (b. 1933)