TI  - Specific activation of  <prot>cdc25</prot> tyrosine phosphatases  by  B-type cyclins: 
      evidence for multiple roles of mitotic cyclins.
PG  - 1181-94
AB  - Two previously unidentified human <prot>cdc25</prot> genes have been isolated, <prot>cdc25A</prot>
      and <prot>cdc25B</prot>. Both genes rescue a cdc25ts mutant of fission yeast.
      Microinjection of anti-<prot>cdc25A</prot> antibodies into HeLa cells causes their
      arrest in mitosis. <prot>cdc25A</prot> and <prot>cdc25B</prot> display endogenous tyrosine
      phosphatase activity that is stimulated several-fold, in the absence of
      cdc2, by stoichiometric addition of either <prot>cyclin B1</prot> or B2 but not A or
      D1. Association between  <prot>cdc25A</prot>  and  <prot>cyclin B1</prot>/<prot>cdc2</prot>  was detected in the HeLa
      cells. These findings indicate that   B-type cyclins   are multifunctional
      proteins that not only act as M phase regulatory subunits of the  <prot>cdc2</prot>
      protein kinase , but also activate the  <prot>cdc25</prot> tyrosine phosphatase , of which
      <prot>cdc2</prot> is the physiological substrate. A region of amino acid similarity
      between cyclins and tyrosine PTPases has been detected. This region is
      absent in <prot>cdc25</prot> phosphatases. The motif may represent an activating domain
      that has to be provided to <prot>cdc25</prot> by intermolecular interaction with <prot>cyclin B</prot>.
AD  - Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, New York
