An improved gene splicing and recombinant plasmid transformation method is described. The method includes mechanical fragmenting of chromosomal DNA followed by conventional digestion with a restriction enzyme and gene splicing into a vector to provide recombinant plasmids in a bank of at least about 100 different plasmids. The plasmids in the bank are provided for transformation into a suitable host, particularly a plasmid free bacterium of the same species from which the chromosomal DNA or the vector is derived. The method provides high transformation frequencies because of the presence of multiple "super coiled" or closed coiled recombinant plasmids in the bank. The method also allows for the direct selection of many different phenotypic traits in a pool of the transformed hosts. The selected hosts are useful for the production of various gene products.
