High Quality Content by WIKIPEDIA articles! In molecular biology, DNA ligase is a specific type of enzyme, a ligase, (EC 6.5.1.1) that repairs single-stranded discontinuities in double stranded DNA molecules, in simple words strands that have double-strand break (a break in both complementary strands of DNA). Purified DNA ligase is used in gene cloning to join DNA molecules together. The alternative, a single-strand break, is fixed by a different type of DNA ligase using the complementary strand as a template, but still requires DNA ligase to create the final phosphodiester bond to fully repair the DNA.