ALB and infection: A proportion of the viral particles released from the dual-infected cell lines contain one RNA from each provirus (heterozygous viruses); recombination between which can occur during reverse transcription to generate a recombinant progeny expressing a functional gfp. The multiplicity of infection (MOI) of the GFP+ events, as a percentage of the total infection MOI (determined using the expression of HSA and Thy), provides a measure of the recombination efficiency between the two viruses.