Final answer:
DNA ligase's function is to join two pieces of DNA, such as a plasmid and foreign DNA cut with the same restriction enzyme, and is not selective for recircularizing plasmid DNA containing only the gene of interest.
Step-by-step explanation:
In the process of gene cloning, DNA ligase plays a crucial role, but it is not selective for only recircularizing plasmid DNA containing a gene of interest. Rather, DNA ligase's function is to join together two pieces of DNA to form a stable molecule. Both the foreign DNA and the plasmid are cut by the same restriction enzyme that recognizes specific DNA sequences known as restriction sites. In the context of cloning, if the foreign gene is inserted into the plasmid where it disrupts a gene such as the lacZ gene, this can be later identified by changes in phenotype or by using other genetic markers such as antibiotic resistance.
To successfully insert a gene of interest into a plasmid, both must be cut with a restriction enzyme that produces compatible ends. Once the foreign DNA is inserted within the cut plasmid, DNA ligase is used to 'paste' the DNA fragments by forming covalent phosphodiester bonds, effectively ligating the inserted DNA with the plasmid DNA. This ligated plasmid can then be introduced into a bacterial host for replication and protein expression. If performed accurately, it allows only the cells transformed with the recombinant plasmid to grow when cultured with a selective marker like an antibiotic.