Alternate polyadenylation in rodent cells results in two differentially expressed cyclin B1 mRNAs

Cyclin B1 is required for the G2/M transition. In HeLa cells, the level of both its protein and mRNA varies dramatically through the cell cycle. In this study we examine the expression of cyclin B1 mRNA in Chinese hamster ovary cells and 3.7, a transformed rat embryo fibroblast line. In contrast to HeLa cells in which a single transcript is seen, both of these lines express two distinct transcripts of approximately 1.4 and 2.7 kbp in length which appear to be made using different polyadenylation sites. In CHO cells, the level of the upper band varies modestly through the cell cycle while the lower band remains almost constant. In contrast to HeLa cells, CHO cells in G1 express a significant amount of cyclin B1 mRNA. In synchronized 3.7 cells, the level of both transcripts is very low in G1 and rises in parallel as cells progress through S and G2, but the longer transcript disappears faster as cells reenter G1.