FIG. 1.

(A) Serum induction of cdc25A mRNA in NIH 3T3 cells. NIH 3T3 cells were serum starved for 48 h and induced with serum for the time periods (in hours) indicated above the lanes. Total RNA was isolated and analyzed by RNase protection for cdc25A, cyclin E, and ARPP-P0 as described in Materials and Methods. The areas of separate gels with specifically protected bands are shown. (B) The cell cycle phase of serum-starved and -induced NIH 3T3 cells was determined by propidium iodide staining and flow cytometry.