Purification of a terminal uridylyltransferase that acts as host factor in the in vitro poliovirus replicase reaction

Poliovirus RNA polymerase requires a host factor to initiate RNA synthesis in vitro. The host factor was previously purified to near homogeneity from HeLa cells but was not assigned an enzymatic activity. This report describes the purification of a terminal uridylyltransferase that can act as host factor. By all criteria examined it is identical to the factor purified previously. It has the same molecular weight (68,000), chromatographic properties, and cellular localization. We present evidence that terminal uridylyltransferase can add uridine residues to the 3' poly(A) end of virion RNA and that these anneal back to the poly(A) and form a hairpin primer for polymerase.