Practice question

pBR322 is one of earliest low-copy artificial cloning plasmids derived from pMB1, constructed by Bolivar and Rodriguez. It contains pMB1 origin replicating in Escherichia coli, restriction sites clustered in antibiotic genes. Antibiotic resistance determinants include bla gene encoding beta-lactamase conferring ampicillin resistance and tet gene encoding tetracycline efflux pump conferring tetracycline resistance. Inactivation mapping allows selection: insertion in one resistance gene renders recombinant sensitive to corresponding antibiotic while retaining resistance to the other, enabling insertional marker selection. This dual marker system was foundational for recombinant DNA technology teaching.