Which option is correct about T4 DNA ligase?

Correct answer: It joins DNA fragments in cloning by forming phosphodiester bonds between their ends.

T4 DNA ligase joins DNA fragments by forming phosphodiester bonds between 3′-OH and 5′-phosphate ends. Therefore, it is used in recombinant DNA and cloning experiments to join vector DNA with foreign DNA. Option B describes a restriction endonuclease, which cuts DNA. Exam tip: remember, ligase joins DNA, whereas restriction enzymes cut DNA.