URA3+ colonies from the Zorro3 retrotransposition assay. An example of a retrotransposition assay plate. C. albicans ura3- strain CAI4, transformed with a construct containing a wild-type tagged Zorro3 element, was plated onto medium lacking uridine. The photo shows the plate after 3 weeks incubation at 22°C. No colonies were ever observed when parental (non-transformed) CAI4 was tested under identical condiions.