A cysteine-rich motif in poliovirus protein 2CATPase is involved in RNA replication and binds zinc in vitro

Protein 2C(ATPase) of picornaviruses is involved in the rearrangement of host cell organelles, viral RNA replication, and encapsidation. However, the biochemical and molecular mechanisms by which 2C(ATPase) engages in these processes are not known. To characterize functional domains of 2C(ATPase) we have focused on a cysteine-rich motif near the carboxy terminus of poliovirus 2C(ATPase). This region, which is well conserved among enteroviruses and rhinoviruses displaying an amino acid arrangement resembling zinc finger motifs, was studied by genetic and biochemical analyses. A mutation that replaced the first cysteine residue of the motif with a serine was lethal. A mutant virus which, lacked the second of four potential coordination sites for zinc was temperature sensitive, At the restrictive temperature, RNA replication was inhibited,whereas translation and polyprotein processing, assayed in vitro and in vivo, appeared to be normal. An intragenomic second-site revertant which reinserted the missing coordination site for zinc and recovered RNA replication at the restrictive temperature was isolated. The cysteine-rich motif was sufficient to bind zinc in vitro, as assessed in the presence of 4-(2-pyridylazo)resorcinol by a colorimetric assay. Zinc binding, however, was not required for hydrolysis of ATP. 2C(ATPase) as web as its precursors 2BC and P2 were found to exist in a reduced form in poliovirus-infected cells.