RESUMEN
We have mapped the vaccinia virus (VV) gene encoding the large subunit of ribonucleotide reductase (VV M1) within the HindIII I restriction fragment by using an oligonucleotide probe. Nucleotide sequencing revealed a 2340-bp open reading frame (orf), 1-3, whose amino acid sequence is highly homologous to the mouse M1 protein. The 1-3 gene was expressed as an immediate-early gene product, being transcribed in a leftward direction into a 2.7-kb polyadenylated transcript. Hybrid-selected translation of cycloheximide-amplified immediate-early viral RNA demonstrated that this mRNA encoded an 86-kd protein, which agrees with the expected size of the reductase large subunit. The 5'- and 3'-boundaries of the 1-3 transcriptional unit were determined by primer extension and S1-nuclease analysis, respectively, and shown to contain sequence elements typical of other VV early genes. Surprisingly, the predicted amino acid sequence of the VV enzyme subunit shares 72.5% homology with the mouse large subunit, M1.