Disclosed are novel checkpoint polynucleotides encoding polypeptides designated Rad1, polypeptides encoded by the polynucleotides, expression constructs comprising the polynucleotides, host cells transformed or transfected with the polynucleotides, methods for producing the polypeptides, antibodies immunospecific for the polypeptides, methods to identify binding partners of the polypeptides, and methods to screen for modulators of Rad1 biological activity.
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