DNA analysis in the initial DNA cloning experiments. (Top) Agarose-gel electrophoresis of (lane a) the pSC102 plasmid containing three of the multiple EcoRI-generated fragments of R6-5 DNA (lane b). Lane c shows that EcoRI cleavage of the pSC101 vector produces a single DNA fragment of the expected size. (Middle) Electron photomicrograph of pSC101, the first plasmid used successfully as a vector for DNA cloning. (Bottom) Agarose gel electrophoresis showing cloning of the kanamycin resistance gene of R6-5: (lane d) EcoRI-cleaved DNA of the pSC101 plasmid vector, (lane c) EcoRI-generated fragments of a novel plasmid (pSC102) that had been constructed from R6-5 (see Top) and that expresses the kanamycin resistance determinant of the parental R6-5 replicon, (lane b) mixture of the DNAs shown in lanes c and d, and (lane a) EcoRI-generated fragments of a novel plasmid (pSC105) expressing both the tetracycline resistance gene of the pSC101 vector and the kanamycin resistance gene, which had been cloned from pSC102 by attaching it to pSC101. Top and Bottom are from ref. 1.