FIG. 9.

Proposed model for poliovirus RNA minus-strand RNA synthesis compared to that of hepatitis B virus and adenovirus. Poliovirus minus-strand synthesis might resemble that used by hepatitis B virus (60) and adenovirus (25). Both DNA and RNA synthesis takes place in three consecutive steps: protein priming, jumping back, and elongation. Poliovirus 3D^pol complexed with VPg and 3CD^pro binds to the cre(2C) RNA (19). RNA polymerase 3D^pol catalyzes the covalent linkage of UMP to VPg using the first two A's of the conserved AAACA sequence of the cre(2C) RNA as a template. The complex of 3D^pol and VPgpUpU is released and translocated to the 3′ end of the poly(A) tail. The precursor VPgpUpU then serves as primer for minus-strand RNA synthesis. Abbreviations: RT, reverse transcriptase; pTP, preterminal protein; DP, DNA polymerase.