Functional analysis of the P box, a domain in cyclin B required for the activation of Cdc25

Xiao Feng Zheng, Joan V. Ruderman

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69 Scopus citations


Cyclin B-cdc2 complexes are kept inactive by inhibitory phosphorylations on Thr-14 and Tyr-15 of cdc2 until they are dephosphorylated at the end of G2 by the phosphatase cdc25. Recent work has suggested that a small region of cyclin B, which we call the P box, may contribute part of a phosphatase-activating domain to cdc25. Individual conservative substitutions at three invariant residues within the P box yield mutant cyclin B proteins that bind cdc2 in vitro and then show the predicted cell cycle arrest, with cdc25 remaining in the low activity interphase form and cyclin B-cdc2 complexes remaining phosphorylated and inactive. While the low activity interphase form of cdc25 cannot act on cdc2 complexed with a mutant P box cyclin, the high activity M phase form of cdc25 can. These results demonstrate that the P box domain of cyclin B is required for cdc25 activation and support a two-step mechanism for the cdc25-dependent activation of cyclin B-cdc2.

Original languageEnglish (US)
Pages (from-to)155-164
Number of pages10
Issue number1
StatePublished - 1993
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Biochemistry, Genetics and Molecular Biology


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