Yen J Y, Kellems R E
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030.
Mol Cell Biol. 1987 Oct;7(10):3732-9. doi: 10.1128/mcb.7.10.3732-3739.1987.
Multiple dihydrofolate reductase (dhfr) mRNAs, differing substantially in abundance, are produced as a result of the utilization of multiple transcription initiation sites and multiple polyadenylation sites. We have shown that dhfr mRNAs initiating from an upstream promoter region utilize the same collection of six polyadenylation sites and generate multiple dhfr mRNAs at the same relative abundance as do the mRNAs initiating from the major transcription promoter region. These results indicate that the 5' and 3' ends of dhfr mRNAs are independently determined. We show that the relative abundance of steady-state dhfr mRNAs was the same in nuclear and cytoplasmic RNA fractions. This finding makes it unlikely that differences in mRNA stability account for differences in the relative abundance of the multiple dhfr mRNAs in the cytoplasm. Our analysis of the dhfr promoter region revealed the existence of stable cytoplasmic polyadenylated transcripts complementary to the first 300 nucleotides of the dhfr transcripts initiating from the upstream promoter region. Therefore, the dhfr locus hosts two divergent and partially overlapping genes which share the same promoter region.
由于使用了多个转录起始位点和多个聚腺苷酸化位点，产生了丰度差异很大的多种二氢叶酸还原酶（dhfr）mRNA。我们已经表明，从上游启动子区域起始的dhfr mRNA利用相同的六个聚腺苷酸化位点集合，并产生与从主要转录启动子区域起始的mRNA相同相对丰度的多种dhfr mRNA。这些结果表明，dhfr mRNA的5'端和3'端是独立确定的。我们表明，稳态dhfr mRNA在核RNA和细胞质RNA组分中的相对丰度相同。这一发现使得mRNA稳定性的差异不太可能解释细胞质中多种dhfr mRNA相对丰度的差异。我们对dhfr启动子区域的分析揭示了存在与从上游启动子区域起始的dhfr转录本的前300个核苷酸互补的稳定细胞质聚腺苷酸化转录本。因此，dhfr基因座包含两个不同且部分重叠的基因，它们共享相同的启动子区域。
