PCS101

This earliest plasmid vector contains the replication module for replication in E.coli gene for resistance tetracycline and single recognition sites for restriction. Insertion of DNA insert into the ECoR1 site leaves the gene in act and functional as a result E. cells transformed by psc101 become the DNA insert or a recombinant one on the other hand insertion of DNA fragment into the Hind111 Bam H1 or Sal sites disrupts the gene and makes it nonfunctional. Therefore, cells transformed by such a recombinant are sensitive to tetracycline and hence can be easily distinguished from those containing the non recombinant plasmid which are resistant to the antibiotics.
But non transformed cells too are tetracycline sensitive hence they can not be separated from those having the recombinant.
Clearly pSC101 does not permit a direct selection of cells containing the recombinant vector. In addition, it contains unnecessary DNA, and has stringent regulation of replication. Subsequently, ser=veral novel plasmid vector were designed to over come these deficiencies.