Belongs to the ribonucleoside diphosphate reductase small chain family. Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. Inhibits Wnt signaling.it have two regulatory sites: the specificity site, which controls substrate specificity, and the activity site which regulates overall catalytic activity. A substrate-binding catalytic site, located on M1, is formed only in the presence of the second subunit M2.