The present invention is related to integrated method and tools to construct recombinant DNA molecules (to be used as DNA vaccine or gene therapy) without requiring the use of antibiotic(s) resistance gene(s) and without requiring the addition of one or more antibiotic(s) to the culture medium of cells submitted to this recombinant DNA method. The present invention allows to obtain the selection of recombinant host cell(s) transformed by a (exogenous) nucleic acid sequence of interest (extra-chromosomal vector containing the insert) and simultaneously stabilization (stable inheritance) of this (exogenous) nucleic acid sequence of interest into the transformed host cell(s) descendants (maintenance of the nucleic acid sequence of interest in the host cells population).