Ribonucleoside-diphosphate reductase functions as a heterodimer of a large and a small subunits in deoxyribonucleotide synthesis. RRM1 constitutes to the large subunit (R1) of ribonucleotide reductase,and it can either form heterodimer with small subunit RRM or RRM2B. RRM1 provides the precursors necessary for DNA synthesis. RRM1 can not be detected in quiescent cells,while its mRNA and protein are present throughout the cell cycle in cycling cells. Researches showed that RRM1 is involved in carcinogenesis,tumor progression,and the resistance of non-small-cell lung cancer (NSCLC) to treatment. Low level expression of RRM1 in NSCLC is associated with poor survival.