Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey 08855-0759.
Reovirus mRNAs synthesized by the virion-associated RNA polymerase contain a 5'-terminal cap that is added to nascent transcripts by polypeptide lambda 2, a structural component of virions encoded by double-stranded RNA genome segment L2. The complete, 3916-nucleotide sequence of a full-length reovirus type 3 L2 DNA clone was determined by the dideoxy chain terminator method. The sequence has a single long open reading frame extending from the second A-T-G at nucleotide 14 to a termination codon at position 3881. On this basis, the 1289-amino acid sequence of polypeptide lambda 2, the reovirus mRNA guanylyltransferase, was deduced and compared to other GTP-binding proteins. Two different, lysine-containing lambda 2 peptide sequences closely resemble predicted amino acid stretches in vaccinia virus guanylyltransferase and potentially form part of active sites in the viral mRNA capping enzymes.