Fig. 4
From: An overview on current molecular tools for heterologous gene expression in Trichoderma
Gene deletion and marker recycling using a bidirectional marker. A The target gene is deleted using a homologous recombination (HR) strategy. A double cross-over must occur between the homologous sequences flanking the target gene (3′ and 5′ flanking regions, FR). The pyr2 or pyr4 gene replaces the target gene and restores uridine-prototrophy in an auxotrophic recipient strain. B For marker recycling, an internal cross-over between direct repeats (DR) flanking the marker gene needs to occur, resulting in 5-FOA resistance