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Abstract:
Mad2 is a key component of the spindle checkpoint, a device that
controls the fidelity of chromosome segregation in mitosis. The ability
of Mad2 to form oligomers in vitro has been correlated with its ability
to block the cell cycle upon injection into Xenopus embryos. Here we
show that Mad2 forms incompatible complexes with Mad1 and Cdc20, neither
of which requires Mad2 oligomerization. A monomeric point mutant of Mad2
can sustain a cell cycle arrest of comparable strength to that of the
wild-type protein. We show that the interaction of Mad2 with Mad1 is
crucial for the localization of Mad2 to kinetochores, where Mad2
interacts with Cdc20. We propose a model that features the kinetochore
as a 'folding factory' for the formation of a Mad2-Cdc20 complex endowed
with inhibitory activity on the anaphase promoting complex.
