Practice question
Question
In pBR322, insert in PstI site disrupts which gene?
Explanation
pBR322, an early synthetic plasmid of 4361 bp, possesses two antibiotic resistance genes: amp encoding β-lactamase and tet encoding tetracycline efflux pump. PstI recognition site CTGCAG lies within coding sequence of amp gene at position 3609, while BamHI and SalI reside within tet. Cloning foreign DNA into PstI site interrupts ampicillin resistance determinant through insertional inactivation, rendering recombinants sensitive to ampicillin but retaining tetracycline resistance. This differential antibiotic phenotype historically enabled recombinant identification before lacZ blue-white system became widespread for easy screening.
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