The conserved nonanucleotide motif of the geminivirus stem-loop sequence promotes replicational release of virus molecules from redundant copies.

Recombinant plasmids containing head-to-tail copies of different coat-protein replacement genomes of wheat dwarf virus (WDV) were used to study the mechanism leading to the release of replicating unit-length molecules in suspension culture cells of Triticum monococcum. For plasmids bearing two complete genomes, the viral unit bracketed by the two large intergenic regions (LIR) becomes preferentially released. Addition of a third copy of the LIR on the inoculum plasmid is necessary for release of both WDV genomes with the same efficiency. Using plasmids containing a single viral genome flanked by two different hybrid LIRs, we show that the sequence TAATATTA, which is part of the conserved geminivirus nonanucleotide motif of the potential hairpin structure, is the region of the LIR within which the release of unit-length molecules occurs. Moreover, the data suggest that this release results primarily from rolling-circle replication, also in situations where intramolecular homologous recombination is simultaneously possible.