Genetic reagents for generating plasmids containing multiple copies of DNA segments

Genetic reagents for generating plasmids containing multiples of a DNA segment are prepared by modification of the restriction sites of plasmid rings. The modified plasmids permit cloning of DNA segments which can be recovered with sticky ends that are complementary but not rotationally equivalent. Such segments will polymerize in a head-to-tail conformation. The plasmid rings with modified restriction sites are also used in linear form to obtain head-to-tail joining of multiple DNA segments into plasmid rings for further cloning and/or expression of the DNA segment-directed protein. The critical restriction site sequences of the modified plasmid rings can be prepared as a reagent which permits the sequence to be introduced into any plasmid. The reagents have utility in preparing multiples of protein-forming genes, and in preparing large amounts of homogeneous DNAs which can themselves be used as reagents.