Cyclin a

Cyclin A is a member of the cyclin family, a group of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes. Cyclin A is unique in that it can activate two different CDKs, CDK1 and CDK2, and is involved in both the S phase and the G2/M transition of the cell cycle.

Function

Cyclin A plays a crucial role in the regulation of the cell cycle. It is synthesized during the S phase and is required for the initiation and progression of DNA replication. Cyclin A binds to and activates CDK2, which in turn phosphorylates target proteins necessary for DNA synthesis. As cells progress to the G2 phase, Cyclin A associates with CDK1, facilitating the transition to mitosis.

Regulation

The levels of Cyclin A are tightly regulated within the cell. Its expression is controlled by transcription factors such as E2F and is subject to degradation by the ubiquitin-proteasome pathway. The degradation of Cyclin A is mediated by the anaphase-promoting complex (APC), which targets it for ubiquitination and subsequent proteolysis.

Clinical Significance

Abnormal regulation of Cyclin A can lead to uncontrolled cell proliferation and is often associated with various types of cancer. Overexpression of Cyclin A has been observed in tumors of the breast, lung, and colon, among others. As such, Cyclin A is considered a potential biomarker for cancer diagnosis and prognosis.

Related Proteins

Cyclin A is part of a larger family of cyclins, which includes Cyclin B, Cyclin D, and Cyclin E. Each of these cyclins has specific roles in different phases of the cell cycle and interacts with distinct CDKs.

See Also

• Cell cycle
• Cyclin-dependent kinase
• S phase
• G2/M transition
• Anaphase-promoting complex
• Ubiquitin-proteasome pathway
• Cancer