Double strand break (DSB) repair in Cyanobacteria: Understanding the process in an ancient organism.

Cyanobacterial species, Anabaena/Nostoc and Chroococcidiopsis are highly radio-resistant indicating the presence of a robust DNA repair system. However, unlike the establishment of multiple DNA repair pathways in the radio-resistant Deinococcus, research on DNA repair in cyanobacteria has lagged far behind. Being ancient organisms, it is likely that the DNA repair mechanisms have evolved from cyanobacteria to the modern day bacteria. This review focuses on identifying and collating information on the major DNA repair proteins in cyanobacteria including re-annotation of recR and ndk, using Anabaena/Nostoc sp. strain PCC7120 as a model organism. Unlike most other bacteria, the DNA repair genes of cyanobacteria are not clustered in operons. Though the functional characterisation of most DNA repair proteins is lacking in cyanobacteria, a bioinformatic approach using sequences of DNA repair proteins from Anabaena PCC7120, has helped identify the possible protein-protein interactions, and build probable pathways of double strand break (DSB) repair. The emerging picture can be used as a guide to discern the biochemical and physiological roles of the different DNA repair proteins in Anabaena or Synechocystis, which can be manipulated genetically and establish the different DNA repair pathways in cyanobacteria, and their evolution with time.