Arrest states in a set of mutants of rat 3Y1 cells temperature‐sensitive for entering S phase

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Abstract
Four temperature‐sensitive (ts) mutants of rat 3Y1 cells (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) are arrested at 39.8°C mainly with a 2N DNA content (temperature‐arrested cells). The states of these cells were compared with findings in case of cells arrested at 33.8°C at saturation density (density‐arrested cells), with regard to the ability to enter S phase after release from arrest or after serum stimulation at 39.8°C. With the 3Y1tsD123, the ts defect is an event which seems essential for the initiation of S phase and occurs after mitosis but not after release from the density arrest. The defect in 3Y1tsF121 related to the efficiency of utilization of serum component(s). In case of 3Y1tsG125, the state of temperature arrest appeared to locate between the state of density arrest and the beginning of S phase. There was no significant difference between the density‐ and the temperature‐arrested cells, in case of 3Y1tsH203.