Sic1, a protein, is a stoichiometric inhibitor [1] of Cdk1-Clb (B-type cyclins) complexes in the budding yeast Saccharomyces cerevisiae. Because B-type cyclin-Cdk1 complexes are the drivers of S-phase initiation, Sic1 prevents premature S-phase entry. [2]

Feb 7, 2011 · SIC1 encodes a cyclin-dependent kinase inhibitor (CKI) that regulates the cell cycle at the G1 to S transition by inhibiting the activity of the cyclin-dependent kinase (CDK) Cdc28p (5 and reviewed in 13 and 14). Sic1p is a potent inhibitor of the cyclin-CDK complexes containing a B-type (Clb) but not a G1 (Cln) cyclin (3, 18).

Oct 3, 2016 · Traversal from G1 to S-phase in cycling cells of budding yeast is dependent on the destruction of the S-phase cyclin/CDK inhibitor SIC1. Genetic data suggest that SIC1 proteolysis is mediated by the ubiquitin pathway and requires the action of CDC34, CDC4, CDC53, SKP1, and CLN/CDC28.

Unphosphorylatable Sic1 was abundant and nuclear throughout the cell cycle and effectively inhibited Clb kinase in vitro. SIC1-0P cells had a lengthened G 1 and increased G 1 cyclin transcriptional activation and variable delays in the budded part of the cell cycle.

In Saccharomyces cerevisiae, Sic1, an inhibitor of Cdk (cyclin-dependent kinase), blocks the activity of S-Cdk1 (Cdk1/Clb5,6) kinase that is required for DNA replication. Deletion of Sic1 causes premature DNA replication from fewer origins, ...

Sic1 is an intrinsically disordered protein and achieves its inhibitory function by cooperative binding, where different structural regions stretch on the Cdk1/Clb surface. Moreover, Sic1 promotes S phase entry, facilitating Cdk1/Clb5 nuclear transport, and therefore revealing a double function of inhibitor/activator that rationalizes a ...

Feb 7, 2011 · Sic1 binds Cdc4 in a highly dynamic complex. The intrinsically disordered cyclin-dependent kinase inhibitor Sic1 contains several different Cdc4-binding sites.

May 4, 2011 · Sic1 is an example of IDP populating collapsed states of particularly high compactness. Nevertheless, compact states are destabilized in the isolated C-terminal fragment, relative to the native protein.

In this study, we describe the identification of protein domains by the heterologous expression, purification, and characterization of Sic1-derived fragment. Four C-terminal fragments (Sic1(C-ter)) were produced based on functional studies and limited-proteolysis results.

In the yeast Saccharomyces cerevisiae, Sic1, an inhibitor of Clb-Cdc28 kinases, must be phosphorylated and degraded in G 1 for cells to initiate DNA replication, and Cln-Cdc28 kinase appears to be primarily responsible for phosphorylation of Sic1.