CLB1

CLB1 is a gene in the budding yeast Saccharomyces cerevisiae that encodes a B-type cyclin. The Clb1 protein binds to the cyclin-dependent kinase Cdc28 to form an active mitotic cyclin-CDK complex, which drives progression through late G2 and mitosis. As part of the mitotic machinery, Clb1-CDK activity contributes to proper spindle dynamics, chromosome alignment, and nuclear division, and it participates in the regulation of mitotic exit.

Functional redundancy with related cyclins is a notable feature of CLB1. Clb1 shares overlapping roles with its paralog CLB2, and genetic analyses show that CLB1 is not essential on its own, whereas cells lacking both CLB1 and CLB2 display pronounced mitotic defects or lethality. This redundancy reflects the broader role of B-type cyclins in coordinating mitotic events in yeast.

Regulation and expression of CLB1 are cell cycle–coupled. Clb1 protein levels rise during late S phase and peak in mitosis, followed by degradation as cells exit mitosis. The degradation is mediated in part by the anaphase-promoting complex (APC/C), ensuring orderly progression through and completion of mitosis. The transcription of CLB1 is likewise tightly controlled by cell cycle regulators, aligning cyclin abundance with mitotic needs.

Localization studies show Clb1 primarily associates with the nucleus, with distribution patterns that change during the cell cycle to support its mitotic functions. Research on CLB1 has contributed to understanding the specificity and redundancy among B-type cyclins and their roles in eukaryotic cell cycle control.

See also: cyclin-dependent kinases, Cdc28, B-type cyclins, Saccharomyces cerevisiae, cell cycle.

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