Which protein is a regulator of M-Cdk at the M checkpoint?

At the M checkpoint in the cell cycle, the activity of M-Cdk (M-phase cyclin-dependent kinase) is regulated by several proteins. The appropriate regulator at this checkpoint is APC (Anaphase Promoting Complex).

APC is a multi-subunit E3 ubiquitin ligase that plays a critical role in triggering anaphase by promoting the degradation of specific proteins. One of its key functions is to target securin for destruction, thereby allowing the activation of separase, which leads to the separation of sister chromatids. This action is essential to ensure that the cell transitions properly from metaphase to anaphase. Additionally, APC also mediates the degradation of cyclins, including the cyclin associated with M-Cdk, leading to the inactivation of M-Cdk at specific points in the cell cycle.

This regulation is crucial for maintaining the order of mitosis and preventing errors in chromosome segregation, which could lead to genomic instability and tumorigenesis.

In contrast, other options, such as Rb and S-Cdk, are involved in the regulation of the cell cycle at different points rather than specifically regulating M-Cdk at the M checkpoint. Securin is a substrate for APC rather than a regulator of M-C