The M checkpoint operates through a series of tightly regulated processes. When a cell enters mitosis, it pauses at the metaphase stage until all chromosomes are correctly attached to the spindle apparatus. The checkpoint proteins, including MAD2 and BUB3, monitor the attachment of chromosomes. If any chromosome is not properly attached, the checkpoint prevents the cell from progressing to anaphase by inhibiting the Anaphase-Promoting Complex/Cyclosome (APC/C).
