this line , ts-36 , was identified as a g1-specific mutant on the basis of four criteria : prolonged viability at the nonpermissive temperature ( npt ) , the kinetics of cell cycle withdrawal and reentry in temperature shift experiments , the ability of the cells to differentiate at the npt in low-growth medium , and , finally , the observation that , by the criterion of flow microfluorometry , the mutant cells block at the g1 landmark in the cell cycle .
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the
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