Figure 4.

(a) Principle of the yeast screening assay. A strain harbouring an expression vector encoding a TALEN is mated with a strain harbouring a reporter plasmid. The reporter plasmid bears a lacZ reporter gene interrupted by an insert containing a TALEN target site flanked by two direct repeats. Upon mating, the TALEN generates a double-strand break at the site of interest, allowing the restoration of a functional lacZ gene by SSA and enabling the generation of a blue colour in the presence of X-Gal. The colour was quantified and scored as the Afilter value, a parameter correlated to TALEN nuclease activity. (b) Nuclease activity of the AvrBs3 TALEN towards Bs3 homodimeric targets harbouring either T, A, C or G at position 0. Afilter values obtained with the four different Bs3 homodimeric targets are displayed. The dashed line indicates the experimental background level. The obtained values are the average of three independent experiments.