SAMHD1 (SAM domain and HD domain-containing protein 1) is an enzyme with SAM and HD domains, primarily localized in the cell nucleus. This protein regulates cellular dNTP levels by degrading deoxyribonucleoside triphosphates (dNTPs), thus inhibiting the replication of retroviruses like HIV. The expression of the SAMHD1 gene is specific to different cell types, and related gene mutations are associated with the development of autoimmune diseases and cancer.