Characterization of the 3' untranslated region of mouse E2F1 mRNA

The E2F family of transcription factors has been implicated in the regulation of the G1 to S phase transition of the mammalian cell cycle. We have focused on characterizing the cell cycle stage-specific expression of one family member, E2F1. Previous studies indicated that there are two mouse E2F1 (mE2F1) mRNA species whose abundance peaks in early S phase. However, it was unknown as to what constituted the structural difference between the two mE2F1 mRNAs and whether or not they encoded identical proteins. We have now cloned sequences corresponding to the 3' untranslated region (3'-UTR) of the mE2F1 gene. Northern blot analyses using different probes demonstrated that the two E2F1 mRNAs were distinguished by differences in the length of their 3' UTRs. We found that the longer (2.7-kb) mE2F1 mRNA contained two consensus RNA instability elements that the shorter (2.2-kb) mE2F1 mRNA lacked. However, a comparison of the stability of the 2.7-kb and the 2.2-kb mE2F1 mRNAs suggests that both mE2F1 mRNAs are fairly stable, having a half-life of 6-9h in both asynchronously growing cells and in the S phase of synchronized cells. Thus, we have determined that both mE2F1 mRNAs contain the identical coding region of the E2F1 protein and that enforced expression of mE2F1 mRNA should not be hampered by problems with RNA stability.