Since the cloning was done into a single restriction site, the insertion of the fragment was not orientated. The orientation (+), for which the gene is in the proper direction regarding the tipApromoter, will lead to the expression of I-SceI gene in S. ambofaciens whereas the orientation (-) will not. To determine the orientation of the insert, a PCR was carried out with a set of three primers annealing on and beside the insert (Fig 2A). The results showed that all the 49 clones analysed carried the I-SceI gene in the opposite direction of the tipA promoter (Fig 2B, orientation -). In order to put aside a genetic background issue, the same cloning assay was performed in JM101 cells, which have already been used to clone a gene encoding I-SceI under the tac promoter