Figure 1.

CDC2 mRNA levels in untreated and UV-irradiated fibroblasts at different phases of the cell cycle. Northern blot analysis was performed as described in Materials and Methods. The two bands represent two transcripts of 2.0 and 1.4 kb. (A) Induction of the CDC2 gene during the cell cycle in human fibroblasts. Cells were serum starved for either 2 or 14 days and incubated after re-addition of serum for the indicated periods of time. Fib, asynchronous population of fibroblasts. (B) Expression of CDC2 is dependent on the dose and time of UV irradiation. The first two lanes show total RNA from undamaged fibroblasts at 0 and 20 h after serum addition. (C) Northern blot analysis of total RNA from G₀ and S phase fibroblasts, irradiated with a UV dose of 10 J/m² and allowed to repair for the indicated periods of time. In all experiments the nylon membranes were consecutively hybridized with probes specific for the human CDC2 and GAPDH genes.