[4] DNA-joining enzymes: A review

This chapter discusses deoxyribonucleic acid (DNA)-joining enzymes; DNA ligases join together DNA chains by transmuting the high-energy pyrophosphate linkage of a nucleotide cofactor into a phosphoester bond between the 5′-phosphoryl and 3′-hydroxyl termini.

Abstract

Publisher Summary This chapter discusses deoxyribonucleic acid (DNA)-joining enzymes. The first DNA-joining enzymes identified were DNA ligases; they join together DNA chains by transmuting the high-energy pyrophosphate linkage of a nucleotide cofactor into a phosphoester bond between the 5′-phosphoryl and 3′-hydroxyl termini. DNA ligase from Escherichia coli (E. coli) is a single polypeptide chain of a molecular weight of 74,000, and bacteriophage T4 induces a DNA ligase having a single chain with a molecular weight of 68,000. Phosphodiester bond synthesis is coupled to the cleavage of a pyrophosphate bond in nicotinamide adenine dinucleotide (NAD) for the bacterial enzyme and in adenosine triphosphate (ATP) for the phage enzyme. An E. coli ligase joins oligo(dT) that is base paired to poly(dA); it also joins oligo(dA) base paired to poly(dT), but this is a much less favorable reaction. The self-complementary poly[d(A-T)] can fold back upon itself to oppose the ends, and a ligase seals these into closed loop molecules (circles). T4 DNA ligase is a much more permissive enzyme than an E. coli ligase; it catalyzes a number of ligations that cannot be performed with the E. coli enzyme.