A protein covalently linked to poliovirus genome RNA.

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Abstract
Poliovirion [32P]RNA, after digestion with RNase T2, yields mononucleotides and a labeled compound X, which is not negatively charged at pH 5. X contains, relative to the label in virion RNA, 1-2 phosphates and is partially acid insoluble. It can be labeled with tritiated amino acids 3 h after infection [of HeLa cells], is insoluble in chloroform/methanol and can be digested with Pronase. These observations suggest that X is a protein. The protein cannot be removed from the polio genome when the RNA is sedimented through a sucrose gradient in 0.5 M NaCl, heated to 100.degree. C in the presence of sodium dodecyl sulfate followed by sedimentation through a sucrose gradient in 80% dimethylsulfoxide or banded in 4 M cesium trichloroacetate. Digestion of the 32P-labeled protein with Pronase yields 1 major 32P-labeled product, which contains pUp. The protein migrates faster than capsid protein VP4 in a polyacrylamide gel. The genome of poliovirus but not poliovirus mRNA is covalently attached to a small virus-coded protein (MW < 7000), which is named VPg. VPg is probably linked to the 5'' end of the polio genome. Possible functions of VPg in viral replication are discussed.