Cross-over of RNA 3'-phosphate ligase into the DNA world.

Overall Significance/Background The central dogma of DNA enzymology has long held that for two pieces of DNA to be ligated, the respective DNA pieces must bear a hydroxyl on the 3′-end and a phosphate on the 5′-end. All of the other types of DNA ends are considered incorrect or “dirty,” as they cannot be joined by classic DNA ligases. However, intrinsic and extrinsic DNA damage often results in broken DNA with dirty ends. Thus, there are a variety of DNA repair enzymes that function to “clean up” or “heal” such dirty ends to promote the restoration of a continuous DNA phosphodiester backbone. Until now, DNA breaks with phosphate at the 3′-end and hydroxyl at the 5′end also fell into the category of dirty ends. The study in PNAS by Das et al. (1) demonstrates that a recently identified RNAprocessing enzyme, RtcB, can directly ligate a DNA 3′-phosphate end with a DNA 5′OH end (Fig. 1).