Transcriptional regulation of mouse dihydrofolate reductase in the cell cycle.

We have studied transcription of the dihydrofolate reductase gene as cells progress through the cell cycle. We used the techniques of DNA-excess filter hybridization and in vivo pulse labeling of a synchronous population of cells to measure the transcription rate of the dihydrofolate reductase gene in different phases of the cell cycle. Our results indicate that the dihydrofolate reductase gene is cell cycle regulated at the transcriptional level. The transcription rate is low in G1, increases 7-fold at the beginning of S phase, decreases almost immediately thereafter, and remains low throughout the remainder of S and into G2. This cell cycle regulation seen in the G1 to S phase transition is achieved by increasing the rate of transcription from a single promoter region. The fact that this region is similar to promoter regions of other housekeeping genes suggests that this type of regulation may not be unique to dihydrofolate reductase.