The function of RRM2B (ribonucleotide reductase regulatory TP53 inducible subunit M2B, Ensembl gene identifier ENSG00000048392) is as follows. Plays a pivotal role in cell survival by repairing damaged DNA in a p53/TP53-dependent manner. Supplies deoxyribonucleotides for DNA repair in cells arrested at G1 or G2. Contains an iron-tyrosyl free radical center required for catalysis. Forms an active ribonucleotide reductase (RNR) complex with RRM1 which is expressed both in resting and proliferating cells in response to DNA damage. {ECO:0000269|PubMed:10716435, ECO:0000269|PubMed:11517226, ECO:0000269|PubMed:11719458}.