Opposite-strand RNAs from the 5' flanking region of the mouse dihydrofolate reductase gene.

We have characterized a transcription unit in the 5' flanking region of the mouse gene encoding dihydrofolate reductase (EC 1.5.1.3) that is oriented in the opposite direction to that of dihydrofolate reductase transcription. These opposite-strand RNAs are 180-240 nucleotides long, differing in length at their 5' ends. They are abundant in nuclear RNA and are not polyadenylylated. We suggest that the promoter region of the dihydrofolate reductase gene functions in a bidirectional manner to produce both these RNAs and dihydrofolate reductase mRNAs.