Defective DNA replication and repair associated with decreases in deoxyribonucleotide pools in a mouse cell mutant with thermolabile ubiquitin-activating enzyme E1

Upon shift-up in temperature, mouse tsFS20 mutant cells with thermolabile u biquitin-activating enzyme E1 immediately stopped DNA replication and showe d cell cycle arrest in S-phase. In contrast, when the cells were permeabili zed with lysolecithin after culture at the nonpermissive temperature, they exhibited a normal level of repliative DNA synthesis in vitro. In agreement with this, intracellular pools of deoxyribonucleoside triphosphates were s ignificantly reduced in the cells cultured at the nonpermissive temperature . Even under the permissive conditions, tsFS20 cells were more sensitive to hydroxyurea and alkylating agents, and induced less mutation than the wild -type cells. These results suggest that the ubiquitin system affects DNA re plication and repair.