Covalent Attachment of Polyribonucleotides to Polydeoxyribonucleotides Catalyzed by Deoxyribonucleic Acid Ligase

Abstract DNA ligase isolated from Escherichia coli or phage T4-infected E. coli catalyzes the covalent joining of the 5'-phosphate termini of polydeoxyribonucleotides and 3'-hydroxyl termini of polyribonucleotides. This reaction occurs with poly(dA) and poly(A) in the presence of poly(dT). The 5'-phosphate terminus of polyd(A-T) can be linked by an intramolecular reaction to its 3'-hydroxyl terminus substituted with a ribonucleotide. Phage T4-induced DNA ligase also joins poly(dT) to poly(U) in the presence of poly(dA). The joining of 5'-phosphate termini of polyribonucleotides to 3'-hydroxyl termini of polydeoxyribonucleotides was detected only with phage T4-induced DNA ligase. This reaction, however, occurred to a limited extent with poly(dA) substrates containing AMP residues at the 5' terminus in the presence of poly(dT). These results suggest that although DNA ligase from E. coli is incapable of joining RNA to RNA, it is capable of joining 5'-phosphate terminus of a DNA to the 3'-hydroxyl terminus of RNA in addition to the well known joining reaction between DNA to DNA. The phage T4-induced DNA ligase on the other hand joins DNA to DNA, RNA to RNA, and RNA to DNA in all combinations.