The 85-kDa polypeptide previously shown to be associated with the restricted (R) component of the EBV-induced early antigen (EA) complex was subjected to amino acid sequencing analysis. This was accomplished by cyanogen bromide cleavage and by separation of individual peptides by high-pressure liquid chromatography employing reversed-phase C18 column techniques. Two of the isolated peptides, F11 and F13, were subjected to amino acid sequencing and both were found to have significant homology to the postulated protein encoded by the BamHI O right reading frame 2 (BamHI ORF2) of the B95-8 strain Epstein-Barr virus. Computer analysis revealed significant homology between the amino acid sequence of this polypeptide and ribonucleotide reductase, an enzyme previously mapped to this genomic fragment. Amino acid composition analysis also revealed a similar association. These results indicate that the 85-kDa EA(R) polypeptide is associated with a component of the EBV-induced ribonucleotide reductase.