pBR322

There are six key restriction sites inside the AmpR gene.The source of these antibiotic resistance genes are from pSC101 for Tetracycline and RSF2124 for Ampicillin.

[2] The circular sequence is numbered such that 0 is the middle of the unique EcoRI site and the count increases through the TetR gene.

Many other plasmids were artificially constructed to create one that would be ideal for cloning purpose, and pBR322 was found to be most versatile by many and was therefore the one most popularly used.

[4] It has two antibiotic resistance genes, as selectable markers, and a number of convenient unique restriction sites that made it suitable as a cloning vector.

[6][7] A large number of other plasmids based on pBR322 have since been constructed specifically designed for a wide variety of purposes.