p31^Comet Splice Variants Induce Distinct Spindle Assembly Checkpoint Dynamics due to Their Unique N-Termini

The role of p31^Comet in deactivating the spindle assembly checkpoint is well described in the literature; however, the data are all completed using Variant 2 of p31^Comet. p31^Comet is known to be expressed as two different splice variants: Variant 1 and Variant 2. Variant 1 contains an additional 32 N-terminal residues compared to Variant 2. We report that Variant 1 exhibits a reduced ability to bind to MAD2 and thus a reduced ability to induce mitotic progression. Additionally, we show that Variant 1 exhibits reduced stability compared to Variant 2. We further show that Variant 1 is uniquely expressed in the Testes, indicating a potentially unique role of Variant 1 in that organ. Overall, we demonstrate the N-terminus of p31^Comet is capable of modulating p31^Comet activity in mitosis.