Isolation of a human X chromosome-linked gene essential for progression from G1 to S phase of the cell cycle

The tsBN462 cell line, a temperature-sensitive (ts) mutant isolated from the hamster cell line, BHK21/13, cannot progress into S phase at 39.5 °C, following the release from isoleucine deprivation. The mutant cells were transfected with high molecular weight (HMW) DNA from human KB cells, and several human DNA bands were found to be conserved through three cycles of ts⁺ transformation. Conserved human DNA was isolated from the cosmid library of the secondary ts⁺ transformant (K-1-1), using ³²P-labelled total human DNA as a probe. The isolated human DNA covers about 70 kb of human DNA flanked with hamster DNA, and originates from the human X chromosome. The middle part (56 kb) of the isolated human DNA was conserved through the primary, secondary and tertiary ts⁺ transformation, without gross rearrangement.