FIG. 2.

SLBP mRNA is constant during the cell cycle. (A) Total RNA from exponentially growing CHO cells was fractionated into poly(A)⁻ and poly(A)⁺ RNA by chromatography on oligo(dT)-cellulose. A 10-μg amount of total RNA (lane 1), 10 or 20 μg of poly(A)⁻ RNA (lanes 2 and 3), and the equivalent amount of poly(A)⁺ RNA from 10, 20, or 50 μg of total cell RNA (lanes 4 to 6) was resolved by gel electrophoresis, transferred to a nylon membrane, and hybridized with the mouse SLBP cDNA (top), rat GAPDH cDNA (middle), or mouse histone H3-614 gene (bottom). Lane 7 is 10 μg of RNA from mouse myeloma cells. (B) Total-cell RNA was prepared from cells selected by mitotic shakeoff at the indicated times (hours) after plating (lanes 2 to 9). Two independent experiments are shown (lanes 2 to 6 and 7 to 9). Over 80% of these cells entered S phase by 8 h in the first experiment, and 95% of the cells entered S phase in the second experiment, as judged by BrdU labeling. A 10-μg amount of RNA was separated by agarose gel electrophoresis and analyzed as in panel A (lanes 2 to 9). Lane 1 is poly(A)⁺ RNA from the equivalent of 20 μg of total RNA from asynchronous cells.