The temperature-sensitive mutant cell line tsBN2, was derived from the BHK21 cell line and has a point mutation in the RCC1 gene. In tsBN2 cells, the RCC1 protein disappeared after a shift to the non-permissive temperature at any time in the cell cycle. From S phase onwards, once RCC1 function was lost at the nonpermissive temperature, p34(cdc2) was dephosphorylated and M-phase specific histone H1 kinase was activated. However, in G1 phase, shifting to the non-permissive temperature did not activate p34(cdc2) histone H1 kinase. The activation of p34(cdc2) histone H1 kinase required protein synthesis in addition to the presence of a complex between p34(cdc2) and cyclin B. Upon the loss of RCC1 in S phase of tsBN2 cells and the consequent p34(cdc2) histone H1 kinase activation, a normal mitotic cycle is induced, including the formation of a mitotic spindle and subsequent reformation of the interphase-microtubule network. Exit from mitosis was accompanied by the disappearance of cyclin B, and a decrease in p34(cdc2) histone H1 kinase activity. The kinetics of p34(cdc2) histone H1 kinase activation correlated well with the appearance of premature mitotic cells and was not affected by the presence of a DNA synthesis inhibitor. Thus the normal inhibition of p34(cdc2) activation by incompletely replicated DNA is abrogated by the loss of RCC1.
|出版ステータス||出版済み - 5月 23 1991|
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