p73 is a p53 paralog that encodes proapoptotic (transactivation-competent (TA)) 
and antiapoptotic (dominant negative) isoforms. TAp73 transcription factors 
mediate cell cycle arrest and/or apoptosis in response to DNA damage and are 
involved in developmental processes in the central nervous system and the immune 
system. p73 proteins may also play a role in the regulation of cell growth. 
Indeed, p73 expression is itself modulated during the cell cycle and TAp73 
proteins accumulate in S phase cells. In addition, the function of p73 proteins 
is also regulated by post-translational modifications and protein-protein 
interactions in different cellular and pathophysiological contexts. Here we show 
that p73 is a physiological target of the p34cdc2-cyclin B mitotic kinase 
complex in vivo. Both p73beta and p73alpha isoforms are hyperphosphorylated in 
normal mitotic cells and during mitotic arrest induced by microtubule-targeting 
drugs. p34cdc2-cyclin B phosphorylates and associates with p73 in vivo, which 
results in a decreased ability of p73 to both bind DNA and activate 
transcription in mitotic cells. Indeed, p73 is excluded from condensed 
chromosomes in meta- and anaphase, redistributes throughout the mitotic 
cytoplasm, and unlike p53, shows no association with centrosomes. Together these 
results indicate that M phase-specific phosphorylation of p73 by p34cdc2-cyclin 
B is associated with negative regulation of its transcriptional activating 
function.