To determine the missing restriction sites in the E. coli cloning vector pBR322, we need to understand the typical layout and restriction sites present in this commonly used vector. pBR322 contains multiple cloning sites for efficient insertion of foreign DNA.
Key Restriction Sites in pBR322:
- BamHI: Typically located in the tetracycline resistance gene region.
- ClaI: Commonly found near the replication origin.
- PstI: Generally positioned in the ampicillin resistance gene region.
Step-by-step Identification:
- Assess position A: Based on the vector map, the site must be a restriction site that influences tetracycline resistance. In pBR322, BamHI is known to be in this area.
- Assess position B: Located close to the replication origin, which is a common spot for ClaI.
- Assess position C: Situated within the ampicillin resistance region where PstI is usually found.
Thus, correlating the standard locations of these restriction enzymes within pBR322 verifies that the correct sequence of restriction sites is A - BamHI; B - ClaI; C - PstI.
