Phospho-specific antibodies (pAIB1) confirm that AIB1 is phosphorylated on Ser728 exclusively during mitosis.

<p>(A) Confocal microscopy analysis of an asynchonous culture of MCF-7 cells stained with DAPI (blue), anti-pAIB1(S728) (Alexa Fluor 488) and anti-β-tubulin (Alexa Fluor 633) to reveal the mitotic spindle. Scale bar: 10 µm. Only mitotic cells stain positively with pAIB1(S728) antibodies and suggest that pAIB1(S728) is excluded from chromatin. (B) Western blot analysis of MCF-7 cells arrested at mitosis with nocodazole. Cell lysates were probed with the indicated antibodies, revealing that anti-pAIB1(S728) antibodies detect exclusively the slower electrophoretic mobility band.