Vector component ensuring replication:
A cloning vector requires essential modules for propagation, selection and insert accommodation. Origin of replication, ori, is a cis-acting DNA sequence where host replication machinery initiates DNA synthesis, controlling copy number and host range. Without ori, plasmid cannot duplicate and is lost during cell division. Antibiotic resistance gene provides selection, lacZ offers insertional inactivation screening and multiple cloning site provides restriction sites. ori from pMB1, ColE1 or pSC101 determines whether vector replicates in Escherichia coli or broad hosts, ensuring stable maintenance of recombinant molecules.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.