Ribonucleotide reductase is essential for the synthesis of all four dNTPs required for DNA replication. The enzyme is composed of two proteins, R1 and R2, which are both needed for activity. Expression of the R1 andR2mRNAs is restricted to the S-phase of the cell cycle, but the R1 andR2 promoters shownoobvious sequence homologies that could indicate coordination of transcription. Here we study initi-ation of transcription at the natural mouse R2 promoter, which contains an atypical TATA-box with the sequence TTTAAA, using a combination ofin vivo reporter gene assays andin vitrotranscription. .
