[Interactions of human ribosomal protein S3 with undamaged and damaged DNA]

Human S3 protein (hS3) is a structural component of the ribosome, which, in addition to its role in translation, possesses activities typical of some DNA repair enzymes. Recombinant hS3 purified from inclusion bodies and refolded under different conditions was investigated for its ability to bind and cleave oligodeoxyribonucleotide substrates containing different lesions abundant in cellular DNA (apurine/apyrimidine sites, uracil, 8-oxoguanine, 8-oxoadenine, 5,6-dihydrouracil, hypoxanthine). hS3 catalyzed cleavage of apurine/apyrimidine sites through beta-elimination mechanism forming a transient Schiff base covalent intermediate, but did not cleave substrates containing other lesions. Refolding of hS3 in the presence of Fe2+ and S2- ions did not increase its activity, despite the earlier suggestions that this protein could contain an iron-sulfur cluster. Binding of hS3 to DNA ligands containing oxidized and deaminated bases was less efficient than its binding to undamaged DNA. Therefore, the activity of hS3 on apurine/apyrimidine sites is not likely to be involved in the global in vivo DNA repair but could have a role in the repair in some specific locations in the genome.