'Primer alignment-and-extension': a novel mechanism of viral RNA recombination responsible for the rescue of inactivated poliovirus cDNA clones.

Pierangeli, A; Bucci, M; Forzan, M; Pagnotti, P; Equestre, M; Pérez Bercoff, R

In the course of experiments designed to assess the potential role of alternative open reading frames (ORF) present in the 5'-terminal untranslated region (5'-UTR) of poliovirus type 1 (Mahoney strain) genomic RNA, we came across a double mutation that completely abrogated the infectivity of full-length cDNA clones. The infectivity was rescued in trans by cotransfecting COS-1 cells with short RNA transcripts of the wild-type 5'-UTR of poliovirus type 2 Lansing, provided a free 3'-OH was available. Direct sequencing of the viral RNA revealed that the infectious viruses recovered were recombinants Lansing/Mahoney, with variable points of 'crossing-over'. A novel mechanism of RNA-RNA recombination, which we propose to call 'primer alignment-and-extension', is described that would explain the high rate of recombination of RNA viruses observed in natural conditions.