A temperature-sensitive mutation affecting S-phase progression can lead to accumulation of cells with a G2 DNA content

Abstract

Cultures of tsBN75, a temperature-sensitive mutant of BHK 21 cells, show a gradual biphasic drop in [³H]thymidine incorporation together with an accumulation of cells having a G2 DNA content when incubated at 39.5°. However, when higher (41°–42°) nonpermissive temperatures were used, the major block was in S-phase DNA synthesis. The cultures of tsBN75 shifted to 42° at the start of the S phase, cell-cycle progress was arrested in the middle of S, while under these conditions wild-type BHK cells underwent at least one cycle of DNA synthesis. When tsBN75 cells growth-arrested at high temperature with a G2 DNA content were shifted to the permissive temperature (33.5° C), the restart of DNA synthesis preceeded the appearance of mitotic cells. These data suggest that the tsdefect of tsBN75 cells might affect primarily the S phase of the cycle rather than the G2 phase.