Which option is correct for E coli DNA ligase?

Correct answer: It is generally NAD⁺-dependent

E. coli DNA ligase uses NAD⁺ as the energy cofactor while sealing nicks in DNA, so option A is correct. In contrast, many bacteriophage ligases, such as T4 DNA ligase, are ATP-dependent; therefore, option B is a close but incorrect choice for E. coli. Exam tip: commonly remember bacterial DNA ligase as NAD⁺-dependent and T4 ligase as ATP-dependent.