Here we proposed the method that is more convenient than traditional methods, because the PCR products can be cloned directly without concerning the restriction enzyme sites. We have developed this method to construct eukaryotic expression T vectors with XcmI sites,i.e.theT vectors can be used in yeast and mammalian cells(notpublished).This method is based on the restriction enzyme digestion of the recombinant to determine the correct orientation of the insert.