The 'pUC19' plasmid is a widely used cloning vector. A key feature of pUC19 that facilitates the selection of recombinant clones is the presence of: MCQ with Answer and Explanation

Question

The 'pUC19' plasmid is a widely used cloning vector. A key feature of pUC19 that facilitates the selection of recombinant clones is the presence of:

A. The lacZ gene for alpha-complementation (blue-white screening)

B. Multiple origins of replication

C. Genes for nitrogen fixation

D. The rop gene for replication control

Answer: Option A

Solution (By JKSSB Mock Tests)

pUC19 is a small, high-copy-number cloning vector. A crucial feature for selecting recombinant clones is the presence of the lacZ' gene, which codes for the alpha-peptide of beta-galactosidase. The multiple cloning site (MCS) is located within this lacZ' gene. When foreign DNA is inserted into the MCS, it disrupts the lacZ' gene (insertional inactivation). On media containing X-gal and IPTG, colonies with empty vectors turn blue, while colonies with recombinant plasmids (disrupted lacZ') remain white, allowing easy visual selection.

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