FIG. 9.

Scenarios for BSGfV integration in the M. balbisiana nuclear genome. (A) Hypothesis 1: use of Ty3/gypsy retroelement for BSGfV integration. Viral RT leads to a pregenomic viral RNA (step 1) during episomal BSGfV infection. A template switch of retrotransposon RT between pregenomic viral RNA and a replicating Ty3/gypsy RNA may form a chimeric RNA (step 2). This step leads to the rearrangements of BSGfV EPRV: fragmentation, inversion, and duplication. Complete retrotransposition of the Ty3/gypsy element leads to its integration (step 3) into the genome of M. balbisiana (within intron 5 of the mom gene). Subsequent genomic change such as recombination may lead to the structural differences observed between the two alleles 7 and 9. (B) Hypothesis 2: Ty3/gypsy retroelement integrated in the fifth intron of the mom gene (step 5) during retrotransposition. Double-strand break repair could account for illegitimate recombination with the single-stranded DNA template generated during BSGfV reverse transcription and integration of the BSGfV genome (step 6). A subsequent genomic change, e.g., recombination, may have lead to both the fragmentation, inversion, and duplication observed in BSGfV EPRV and the structural differences between the alleles 7 and 9 (step 7).